Jerking off sends a rush of dopamine to the brain... but it's not like cocaine for instance which is a synthetic way of getting it. You experience a subsequent low when you increase dopamine synthetically, but it is not always the case when you do it in a more natural fashion. I personally don't see any sort of consistent difference in terms of jerking off before playing... most times I don't (not for any reason just don't) but the times I have, i haven't noticed a difference. The thing that makes the most difference is whether or not I go to the gym having done a routine that already has me really warm. When I do a good stretching and warmup routine, I feel great... if I don't, it's hit and miss, but the first game is usually pretty shitty because I have to warm up. I hate that feeling personally so I always warm up properly now.
I remember years back when in school the sports coaches of various teams would actually tell the guys whether or not to do it before big matches and such. There were also ongoing debates on it between coaches.
The only organized sport I was in then was wrestling, and if I recall correctly we were told to avoid it (or sex) the day of and before a meet.
Also, it was common knowledge that the Football players used to do coke or amps before games...this was in HS.