[Mike Ricketts]

I was watching the game, and assume the play in question was the one where Ichiro was called out for running lane interference.

The applicable rule says that the batter, when running the last half of the distance between home and first, cannot interfere with the fielder receiving a throw by running outside the running lane. The running lane's left edge is the foul line. A separate line is laid down to mark the right edge. The lane is three feet wide.

The logic behind the rule is that the batter could bunt the ball and, as he runs to first base, watch where the first baseman (or whoever is covering first) is setting up to receive the throw from the vicinity of home plate. The batter then could move into the way of the throw and block it, or the fielder's vision, or otherwise make it difficult for the fielder to catch the throw for an out.

On the play in question, Ichiro hit a chopper that was fielded by the pitcher, if I recall correctly. As he ran to first base, at least one foot was landing in fair territory, so he was outside the running lane. The pitcher's throw was wide right, and sailed past the first baseman.

One of the nuances of the running lane rule is that it doesn't protect the fielder who fields the ball and makes the throw to first. It protects the fielder attempting to receive the throw at first. However, when you explain the rule to your 9 year old son, be sure to leave this part out. Otherwise, he might then ask, "But, why, why, why, on the play we saw, was Ichiro called out when his running outside the lane didn't have anything to do with the pitcher making a bad throw -- and that was why the first baseman couldn't catch it?" If he does ask that question, you'll have to look to someone else for an answer, because I don't have one.