Catchers: Be Sure to Protect Your Hand

Catch long enough and you are sure to take a few foul balls off various unprotected areas of the body.  The proper catching stance coupled with wearing the equipment right will limit a catcher's vulnerability but it certainly will never eliminate it completely.  
One of the biggest dangers a catcher faces is a ball that hits his throwing hand.  Although both arms as well as the upper part of the leg are also exposed, the hand is much more vulnerable to injury because of how the hand is constructed.  There are many small, fragile bones that make up the hand and fingers.  When a fast traveling  baseball meets the hand, the hand is never the winner.  As I said earlier, a catcher will never be able to eliminate the danger completely but there are two techniques that can limit the damage should contact be made.
Make a fist.  Make a loose fist with the thumb tucked in.  The looseness of the fist is very important.  Think of the type of fist one would use to knock on a door.  This is important because if a baseball were to hit a loose fist, the fingers will "give" slightly on impact.  If the fist was a tight one, the fingers would not "give" and would face the full force of the ball.  A bone would be more likely to be broken.  Tucking the thumb inside prevents the ball from hitting the tip of the thumb as well.

This is the area to avoid.  Behind the ankle is
usually the location of choice.

Hide the hand.  If you watch major league catchers you will probably see multiple variations on where they position their bare hand prior to the pitch.  A lot of the positioning depends on personal preference and comfort.  Wherever it is located, the key is to keep it hidden from foul balls.  Many young players are taught to keep the hand behind their back.  I'm not a fan of this position because it tends to throw off a catcher's balance too much.  When no runners are on base, most catchers will keep it close to the ground behind the right ankle.  With runners on base, many catchers will want their throwing hand to be closer to the glove for a quicker catch-and-throw transition.  Placing the loose fist behind the glove as if you were going to "knock" on the back of the glove is the most popular location.  In this location, the hand is closer but it's still protected.  A ball that is fouled off will either go above or below the glove and will not hit the bare hand.  The frequent danger in keeping it in that location occurs when a pitch requires the glove to move in order to catch the ball.  If both hands are set up down the middle and the pitch is thrown up and in, it becomes tougher (and slower) to move both hands up to catch the ball so as to continue hiding the bare hand.  Usually the glove moves to catch the pitch but the bare hand stays put which now exposes it to foul balls.   Most catchers just accept this as just one of many risks associated with catching.
Catching is a great position.  All the action is in front of you and you're involved on every pitch.  It certainly is not easy on the body though and players who catch need to take every precaution they can to keep exposed areas safe.