Wrestling, hockey, boxing, basketball and football for sure, maybe soccer and baseball. Golf and swimming are pretty much the only sports I can think of that wouldn’t use a mouth guard.

Weightlifting
There are dozens of sports that don’t require mouthguards & the thought of proper footballers (soccer) using them is frankly hilarious.

@ucme Why? Soccer players are probably just as likely to catch an accidental elbow to the face as basketball players.

@cheebdragon Let’s just say they’re made of stronger stuff than the guys over the pond.

According to here there’s 16 sports requiring mouth guards. A few on the list I disagree with, but can’t prove that they are wrong!!!
01 – Football
02 – Boxing
03 – Ice hockey
04 – Baseball
05 – Wrestling
06 – Boxing
07 – Lacrosse
08 – Field Hockey
09 – Soccer
10 – Basketball
11 – Water Polo
12 – Handball
13 – Rugby
14 – Karate
15 – Horseback riding
16 – Gymnastics

@LadyMarissa I don’t think I have seen any of those young ladies in gymnastics wearing mouth guards. Maybe the guys? I dunno

@anniereborn I agree & I don’t think I’ve ever seen a horseback rider ever use a guard either. This was the list given in the article that I linked. It wasn’t my list. Just noticed that @ucme took soccer off the list as well, so we’re down to 13

You either use a mouth guard or you don’t, so that pretty much encapsulates every sport.

Mouth guards are used in any sport or situation where you feel there could be some sort of impact to the jaw/teeth in order to reinforce every tooth using all other teeth (basically every tooth will now have the force of a whole set, collectively)

We used to wear them when we would aggie in the park
(if you’re American, aggie means playfully fight)