I am making pitching substitutions but when the game is over, why are all the stats applied to only one pitcher?
It is likely that you are trying to make substitutions using the Starting Lineup.
The Starting Lineup screen should only be used to set the state of the start of the game.
To make defensive substitutions during the game, tap on the position you wish to change in the main scoring screen.
Tapping will bring up a defensive substitution screen that will allow you to select a new player for that position.
After selecting the new player from the list, tap Save on the top right of the Sub Screen.