Use 'a/left arrow' and 'd/right arrow' to move along your crease. Use 'w/up arrow' or 's/down arrow' to run to the other stumps. Press spacebar to swing the bat. If you leave the bat without swinging it, the ball will go into your stumps and you will lose. You can choose to run between stumps but if you stop touching the crease, you will lose.
Don't press anything while you are waiting for the '4 Runs' backdrop to switch back because otherwise it will stuff up the bat and you'll lose.