I wasn't a left-handed pitcher, but I learned the left-handed pickoff move in professional baseball from my good friend Carmen Pignatiello, a Chicago Cubs left-handed reliever.
When it comes to the left-handed pickoff move, most umpires are looking at an imaginary line on a 45-degree angle from the left corner of the pitcher's rubber. If the left hander steps to the left of the line, a balk is called. But many lefties can get away with cheating a little if after the right foot hits the ground, they immediately step and walk toward first base. You want to step, throw, and walk off the mound. Do not give the umpire enough time to look at where you step (which is why you'll want to walk off the mound toward first base).
The key to having a successful left-handed move is to decide whether or not you're going to throw to first base BEFORE you actually come set. This way, you can avoid balking. Only in rare instances, say, if the base runner "tips off" that he might be going on the pitch of if he takes a very large lead should you break the rule and throw over to the bag. But mostly, keep it simple: decide early.
If you can retain your balance until the last moment without bringing your lift knee back past your posting knee, the base runner will have a difficult time reading your move. That's because by lifting your leg straight up in a balanced manner, you don't "project" what you're going to do next – you could be delivering the baseball to home plate or you could be making a throw over to the bag. This will help keep the runner close to the base. Once you cross your knees, however, you have to go home with the pitch. So try to bring your lift knee straight up and down, not side to side.
If you have a deceptive move, I think it's OK to sacrifice "quickness" in your delivery in getting the ball to the plate. If you don't have a deceptive move, it's important to get the ball to home plate in 1.3 seconds or less, just like a right-handed pitcher. Remember: holding runners is important, but getting the hitter out is most important – even for lefties. So be quick to the plate if you don't have a good move.
Avoid tipping off your "intent" by moving your head. Most base runners know that if you are looking at the runner when you start your motion, you're going to the plate. They also know that if you're looking at home plate when you start your delivery, you're likely going to make a throw over to the bag. Work hard on relaxing out there on the mound. Don't be predictable. Use the same head movement all the time.
Some coaches like to teach two and three pickoffs to a base – usually a slow move, a medium-speed move, and a "best" move. I'm not a big fan of this. I teach all my pitchers to use just one move – their best move. HOWEVER, I do think that lefties can utilize a quick "step back" off the rubber with the left foot and throw over to the bag, to keep the runner from cheating. I wouldn't rely on this move as your main pickoff, because it can be stressful on the arm, but it's OK to use it every so often.
Perhaps the best way to work on your move is to practice it in front of a full-length mirror without throwing. This way you can work on the mechanics of the move and train your body to be balanced and deceptive without stressing your arm. Then when you get it to a point where you're feeling comfortable with it, have a friend or sibling stand on first base and yell out whether you're going home or making a throw to first base. Try to get to where the person on first base can't tell which direction you're going. Then you know you've got a great left-handed pickoff move!
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