Yes the certainly do. Not all as the wearing of a "gum sheild"is not mandatory
Since 1850 you've had to wear a mouth guards in boxing matches
Yes it used to be optional but now it is mandatory.
Many players wear socks, stockings, or some other cloth layer under their shin guards to prevent chaffing.
No, it won't do much.
Its really not advisable as the mouth does receive some pretty bad knocks in an average game. Many players at all levels now wear mouth guards because of this. Its advisable to speak to a dentist before making decisions on playing with these braces especially as they may cause a choking incident if dislodged.
Yes. It is a violation of safety laws of the game if a professional player doesnt wear them, hence the ref needs to check before a game starts whether all players are wearing them
It could. The mouth guard can help by taking pressure or force away from the brain area. But mouth guards are made specifically made to help prevent any kind of mouth injury. You shouldn't wear a mouth guard to try to prevent a head injury.
equipment wise there are: helmets (football, baseball/softball ,hockey, lacrosse) men usually wear cups soccer and field hockey there are shin guards baseball players wear guards when hitting to protect the side facing th pitcher football, hockey, and lacrosse players wear all types of padding volleyball players sometimes wear pads on their knees field hockey and female lacrosse players wear eye masks strething can be considered an aid for preventing injuries
Usually you wear a rugby jersey, rugby shorts, rugby socks and boots. Some people like myself wear headgear and 99.999% of people wear mouth guards
Which regulations are prominent depend on what country you are in, and often what state, province and even city you are talking about.
Soccer players must wear a shirt, shorts, socks, shin guards and shoes. Lets look in depth just a bit. Law 4 of the Laws of the Game mandates players wear a jersey or shirt. And shorts. Teams wear matching duds. And both keepers wear something different from the players of either team and from each other and the officials. The shin guards must be "made of a suitable material" and must "provide a reasonable degree of protection" per the rules. Socks or stockings must be pulled up to cover the shin guards. No player may wear anything that is dangerous to himself or another player, and the footwear is inspected to insure any features that provide an increase in traction are "safe" and appropriate. There is a bit more detail offered in the Laws of the Game, and a link is provided.