The NFHS rules (used by 48 states) do not restrict the maximum number of players on a roster. The only real restriction is that you cannot have two players on the field at the same time wearing the same number. Since there are only 99 legal numbers for H.S. football jerseys (1–99 inclusive), if you were to have 100 or more players suit up for a game, you would simply have to be careful when substituting so you do not violate this rule.