Major League Baseball Pitching Eligibility

[tankmjg24]

Hey guys I currently have a bragging rights bet going on with a fellow official of mine. I have searched all over for a rules reference to the situation yet cannot find one. I am hoping that you all can help guide me in finding one.

In Major League Baseball, I say that in order for a player to be eligible to pitch that he must be listed on the official lineup as an eligible pitcher. If he is not listed on the lineup as a pitcher then he cannot pitch. My friend says that no such rule exists and that anyone on the team can pitch.