Watch any game from high school on down to tee ball and you will probably see players in the field who are just standing around and don't seem to be involved in the game even when a ball is hit.
To put it more bluntly -- they are bored.
These players have not been taught the importance (and fun) of playing team defense. Whenever a ball is hit every player on the team should be in a sprint. They are either making the play, backing up the play, backing up a throw, covering a bag, or setting up in a relay position. In fact, we tell our players that they are more important to the team when the ball IS NOT HIT TO THEM.
Look at it this way, if a shortstop makes a bad throw to first, but the right fielder hustles and backs up the throw, the runner will be at first -- it will be a one base mistake. But, if the right fielder does not back up the throw the runner may get to third -- a three base mistake.
Defense is fun when we make the great play, but it can be just as fun when we hustle and keep a teammate's mistake from becoming a two or three base error. Also, when we know that our teammates are going to back us up, it allows us to attempt great catches or throws which makes the game fun to play.
COACHES -- WE TEND TO YELL ABOUT BACKING UP WHEN IT HASN'T BEEN DONE AND IT HAS COST OUR TEAM A RUN. HOW ABOUT YELLING WHEN THE PLAYER HAS BACKED UP AND PRAISING HIS HUSTLE EVEN WHEN HE WASN'T INVOLVED BECAUSE THE PLAY WAS MADE CLEANLY? THE MORE YOU PRAISE GOOD TEAM DEFENSE, THE MORE YOUR PLAYERS WILL HUSTLE ON DEFENSE.