I need an explanation

OK, so I'm switching between the Bucs and the House season finale. While House is on I have Gamecast going. Can someone explain to me how this results in a run:

Sanders grounds into fielder's choice to second, Walker scored, Edmonds out at second.

Lanny just said Jack Wilson made an error, but can someone fill in the blanks for me?

UPDATE: OK, just saw the highlights, thrown away DP ball. So Jack has two hits tonight, but makes another costly mistake in the field. Sheesh, not his year so far, is it?