Umpires (usually) are an extension of the playing field in Major League Baseball. If a ball hits an ump in fair territory, the fielder must be ready to play the ball as if it hit a pebble on the ground, or the second base bag. Reaction time is key. In that vein, if a fielder stumbles during a play and — say — runs into an umpire, he runs the risk of getting elbowed in the face if he's not careful.
That's what happened to Carlos Lee of the Houston Astros after he tried to play a sharp grounder hit by Jimmy Rollins of the Phillies in the first inning Tuesday afternoon. After the ball went off his mitt, Lee's stumbling momentum carried him into first base umpire Hunter Wendelstedt, who tried to brace for impact but was sent tumbling on his backside anyway. But not before he accidentally (it's assumed) stuck an elbow in Lee's left eye.
You see what happens? An elbow for an eye and Carlos Lee goes half-blind. But after trainers checked him out, Lee was back at his position for most of Philly's 4-3 victory in 10 innings. And to his credit, Wendelstedt was back on his feet practically in one motion before he went to check on Lee's condition. Rollins' hit was scored a double.
Lee was a third baseman in the minors with the White Sox in the latter part of the 20th century, so you can see where his ... agility comes from.