Why does my 2D sprite sink into the floor when I hit "play"?

So I’m entirely new at this, and working on a 2D sprite based game. Managed to get my “idle animation” in there, so I know I’m making progress. The problem is when I hit “play” and my sprite sinks down into the floor, even though the “default running sprite”, which activates when I move right or left, is still aligned with the floor. Any tips?