Who's pitching first?
 

Hypothetical question(s): P1 is listed as the starting pitcher in the initial lineup for the visiting team, and bats ninth (No DH). During the top of the first inning, the visiting team puts in a pinch hitter for P1...

1. Is this a legal substitution?
2. May P1 still pitch in the game?

...To continue... P2 pitches in the bottom of the first and loads the bases with nobody out. P3 replaces P2. Without pitching a single pitch, P3 manages to pick off the runners to end the inning. P4 pitches in the second inning and the remainder of the game.

3. Who is the "starting pitcher"?

4. Assuming the visiting team took the lead in the top of the first and maintained the lead for the win, who is the winning pitcher?

Hypothetical question? MLB, NFHS, NCAA, Little league, Dixie, Pony ,American Legion............ What rules are we playing this hypothetical game by?

MLB (NL, no DH)

You can't remove the pitcher until he has pitched to one batter (or retired the side) so you can't pinch hit for him.

If you do pinch hit for him he is out of the game - period - there is no reentry in MLB.

P1 is the starter - the official scorer decides who the winning pitcher would be in your scenario.