Are you talking about the number of players on the field for each game, or the number of "active" players on a squad available to play on any given day?
I'm pretty sure the PA has a rule about no more than 20 players registered as active for any one round. But as no other series (to my knowledge) insists on players being registered to a specific team with no "guesting" allowed, I'm also pretty sure they are the only ones with a limit.
And I suppose if we are going all pedantic in this thread I should point out that the term "man" is used very loosely here and includes men, women, boys, girls and people of indeterminate or undecided sex