Medical Time Out
There is a lot of debate about the MTO rule, and how some players use it to try and stop another player's momentum, or even get their own heads into the right place(Azarenka vs Stephens at the AO).
Some people say that this rule needs to be eliminated, but this could force players who actually did have something wrong with them to have to forfeit a match, even if their aliment would have been completely treatable had they had access to a trainer. For that reason, I don't think that the MTO should be completely eliminated from professional tennis.
I do have a proposal though; the ATP and the WTA should implement a system where calling for a MTO is an automatic point penalty towards the next game. They should also have some sort of scale to where the longer the MTO lasts the more point penalties the player receives towards the next game, and then after a certain amount of time the player has to default the match(I think they already have the defaulting rule, but it needs to be strictly enforced).