[IRISHMAFIA]

Without going through the entire USA code:

Suspension. A team that is determined to be in violation of USA Softball’s
rules and requirements shall forfeit the game being played or the game last
played. An ineligible player shall be suspended from further play in the
tournament and in any subsequent tournament for which he/she may have
qualified by virtue of their play in the tournament in which they were
suspended. A team, team member, manager or team official may be subject
to further penalties

However, this is not an umpire issue. If a team is protesting a player's eligibility in a tournament, the TD should be notified immediately. It is their responsibility to take any necessary action. Otherwise, the umpire should have the team specifically identify the player in question; ask that player for identification (driver license or some other picture ID), note the player's information in the scorebook of the protesting team and for yourself. Inform the protesting team to inform the league coordinator (or whomever) as soon as possible. The umpire should inform his/her assigner, rules interpreter, uic or whomever is the authority for the association