In all walks of life, there are rules. Some are unwritten while some are very much enforced. This is no different for our favourite sports stars, who are also subjected to rules on a daily basis, both on and off the field. Of course, the sports in which they play have rules set, but the rules we will be talking about in this article are ones that are enforced by the clubs, managers, or owners themselves. Rules that often don't have anything to do with the sport itself and can often be seen as a little quirky or downright weird.

Whether it has to do with wacky haircuts, player behaviour or a dress code, there are many rules that athletes must endure that most fans aren't even aware exist. Fans don't tend to pay that much attention to these things, and why should they? Yet for the athletes themselves, some of these rules can be absolute torture. Whether it's because they are banning them from doing things that they like or because the rule actually is ridiculous and they feel aggrieved to have to go along with it, many of these rules frustrate the athletes involved.

Throughout this list, we will be looking at 15 rules that athletes must follow, whether that be the entire team or just one individual, or clauses that have been placed within a contract. All of the rules have one thing in common: the athletes hate having to follow them.

15 15. New York Yankees Appearance Policy

In terms of sports teams, there are few more iconic than the New York Yankees. Known the world over, the Yankees are a symbol that all sports fans are aware of, which is helped by the fact they always wear the same, classic uniform.

With that look becoming one that people were well aware of, the fact that outlandish hairstyles began to creep into the team was something that didn't sit well with the owner at the time, George Steinbrenner. Because of that, he brought in an appearance policy that players must stick to.

All players and coaches are forbidden from displaying facial hair other than moustaches, unless for religious reasons, ensuring the whole team would have a similar appearance.

Maybe the Yankees should move to New England and play at Gilette Stadium!

14 14. A Stink About Pink

The fact that there could actually be rules regarding someone not being able to support the fight against breast cancer is quite surprising. But that is the case in the NFL, and something that DeAngelo Williams found out the hard way. Sadly, in 2014, Williams' mother passed away from breast cancer, something that obviously hit him hard. He quickly decided he wanted to show his support to raise awareness and funds by wearing pink wristbands for the entire season.

The NFL simply said no to this request to wear pink, stating there are no exceptions to the uniform policy.

The NFL only supports breast cancer research for four games in a season. Instead, Williams died the tips of his hair pink in a protest and as a way to support the charity.

13 13. White, Not Cream

Wimbledon is one of tennis' most prestigious tournaments, rich in history and class it is one of the most highly anticipated sporting events of the calendar year, not just within the tennis world. Because it is such a well-respected tournament it shouldn't come as too much of a surprise that there are some rules that take place, with one dating back to the 1800's.

All competitors must be dressed entirely in white throughout play, with a very strong distinction being placed between white and cream.

This rule extends to the tracksuits the players wear as well, although they are allowed a single trim of colour down the outside seam, as long as it is no wider than one centimetre. Yes, it's really that strict.

12 12. No Biting

This shouldn't really need to be a rule for a fully grown adult, as it sounds more like advice suited to a young child. Yet for Barcelona sensation Luis Suarez, that is exactly what his contract states, with a special clause banning him from biting.

While he might be one of the most gifted footballers on the planet, his temper is something that has always let him down.

It has caused him many problems over his career, with biting being one of his major issues.

Suarez has been caught biting on at least three occasions, but that doesn't mean that is all he has done and therefore it is not really a shock that he has this in his clause, whether he likes it or not.

A lot of clubs like to honour their logo. Some place them on the walkway to the field for the players to touch like Liverpool F.C. Others, such as the New York Rangers have the badge on the floor in the dressing room. Either way, it's there to remind the players who they are representing, instilling pride.

John Tortorella, one of the New York Rangers' most famous ever coaches had so much respect for the team's logo that he banned his players and staff from walking on it.

They weren't even allowed going close to the badge on the floor. While there wasn't a specific punishment if you broke the rule, other than a serious screaming match, the rule was enforced nonetheless and players were expected to not be anywhere near it.

10 10. We Dem Boys

The Dallas Cowboys placed a strict rule on their players to behave themselves which includes no drinking, no exotic dance clubs and a midnight curfew after several players enjoyed too much of the Dallas nightlife.

Dez Bryant was one of the many such players who took his fame and fortune a little too far with his nightlife enjoyment.

Players like Dez Bryant forced the club to put the rule in place in order to ensure the players were 100% for games and training. It's quite baffling that this rule is needed, that professional athletes need strict enforcement to behave themselves and know their limits, but apparently, that is the case.

9 9. No Space Travel

In what has to be one of the most bizarre rules to be put on a sportsman, former Sunderland footballer, Stefan Schwarz was given a 'no space travel' clause within his contract, in order to stop him from, well, traveling to space.

Schwarz joined the Black Cats in 1999 and he had expressed an interest in being booked on the first ever commercial passenger flight into space, something that manager Peter Reid clearly didn't approve of. Sadly for the Swedish midfielder, his space dreams were cut as he signed the deal, but thankfully for him, he didn't miss out on any flights but got to play top-level football instead, despite his frustrations at having to sign the deal.

8 8. No Sponsorships

In WWE, the company has many high profile sponsorships from some of the richest companies in the world in order to make a profit for themselves. This makes sense as they are a business. However when it comes to its employees, sponsorships are not allowed.

The wrestlers would have a good chance to make some extra money from sponsored ring gear or wrestling boots. However the company doesn't allow it, mainly because it could cause problems with the sponsors they already have. That might be something that the WWE Superstars can understand.

But the fact that rule doesn't apply to Brock Lesnar might ruffle a few feathers.

He is allowed to show sponsor's logos on his ring gear and this shows clear favouritism to the former UFC star.

7 7. No Children Allowed

As a father wanting to spend time with his son and offer him great experiences, you can't exactly complain about Chicago White Sox's Adam LaRoche for allowing his 14-year-old son to be inside the clubhouse.

However, the clubs former vice president disagreed and banned children from the clubhouse, a decision that enraged LaRoche who was almost prepared to quit the club, walking away from a $13 million contract in his final year. Eventually, people managed to relax and manager Robin Ventura stepped in to ensure that LaRoche wouldn't leave the club, but his son remained banned from the clubhouse.

6 6. NHL Stars Go Thirsty

It is very common for sports stars to enjoy a drink on occasion, some more so than others. But in the NHL, that isn't the case as a collective agreement with the players union that states there should be no drinking during flights to and from games.

But that isn't the only place that NHL players can't enjoy a beverage. Airports, restaurants and hotels are all blacklisted while players are on the road. However the rule can be relaxed if a manager gives the all clear, which does make the whole thing feel redundant. It's likely not something that the athletes will complain about too much, as they are supposed to be staying in good shape to compete, and can drink offseason, so it isn't too much to ask really.

5 5. Twitter Restrictions

In the modern day, using social media is commonplace for pretty much everybody, that includes sports stars. Occasionally, you see these high profile people push the boundaries a little, but most of the time they manage to restrain themselves from becoming too offensive.

Mario Balotelli, on the other hand, was known for not restricting himself in any part of his life, gaining a reputation as a bad boy during his time with Manchester City. From getting into a fight with his manager to lighting fireworks inside his house, Balotelli was known for being ridiculous, some loved it, others hated it. Clearly, AC Milan hated it. When they signed him in 2013 they had it written in his contract that the club would run his social media, he was banned from having any 'outrageous' haircuts as well as attempting to control his alcohol consumption.

4 4. Playing With Food

Sometimes in soccer people like to pull pranks. It's common for most sports but this particular prank could be one of the cruelest, and it involved a rule being placed within a professional contract. Spencer Prior signed for Cardiff City in 2001 and within his contract was an incredibly odd clause. It stated he had to eat a sheep's "family jewels" before he was allowed to play for the first team.

Unsurprisingly, Prior wasn't exactly thrilled about it. For some reason he signed on and agreed to it, and munched away. What he found out afterward was that it was all a prank and the food was actually chicken, but the fact this was even written down and agreed upon is baffling in the first place.

3 3. Flying Commercial

With the amount of money that top sports teams make, you would expect that they will be given all the greatest treatments, which is why it's very unlikely you will find yourself sat next to a Premier League footballer on a plane. Usually, they fly first class or in a private plane. But for the United States' and Canada's Major League League Soccer, the players are forced to fly commercial, mingling with everybody else.

Newer and richer owners of teams are hoping to scrap this rule in the future in order to provide their players with a more relaxing journey to their game. But other teams do not want a change, meaning they will likely have to endure commercial flights a little longer.

2 2. Heyward Can't Honor His Father

It seems that the NFL has a distinct problem with its athletes honouring fallen loved ones, as we have already mentioned on this list, but this rule is even more strange given the people involved. In 2006, Cameron Heyward's father, Craig 'Ironhead' Heyward passed away from cancer. A legend of the game, Craig had been given the nickname 'Ironhead' through football, so Cameron wore black paint under his eyes with the nickname on them as a way to honour him.

Touching, and harming nobody it seemed like a fine tribute to his fallen father in the eyes of everybody, but the NFL. Instead of seeing it as a touching tribute, the NFL fined Cameron $6,000, which is the complete opposite of what he needed during such a tough time, a truly classless act on the NFL's behalf.

1 1. Watch Your Weight

It is quite strange that professional athletes sometimes do not realize that they need to be in the best shape possible in order to perform at their maximum, but Terrance Knighton clearly didn't work that one out. In 2015, the Denver Broncos defensive linesman began to pile on the pounds, something that affected his game and likely his overall health. Gaining over 350 pounds is no small matter and the time fined him $300,000 for it, no small punishment.

Gaining a rather unflattering nickname of 'The Fridge,' it appeared that the fine wasn't enough to help him overcome this problem and it wasn't much longer before he was no longer a member of the Broncos. He was also known as "Pot Roast", which doesn't give his reputation any help.