When Lucy pulled the football away from Charlie Brown, the play did not end, even as Charlie landed on the opposing team. It's still a live ball (think of the 'fake field goal' plays in games).
Charlie Brown was being blamed for the loss in the football game, but it's not his fault. Lucy was the one who pulled the football away from him before he had a chance to kick it. The other characters should have realized this and directed the blame toward Lucy rather than Charlie.