Can someone tell me Why?  

I really don't know if this is why, but when I'm feeling anxious I like to chew gum to get some of the penned up energy out. I can imagine the players nerves waiting for the next play. I wonder if they do this to unlease the nerves so they can consentrate on the game.

Although it would take a real baseball player to answer this question, I know that keeping the mouth moist can be the reason why a lot of players have a habit of chewing and spitting a lot...

It's get really hot and dusty during games, even in domed stadiums, plus the game level adrenalin keeps players so agitated that they must find something to do, and chewing seems to fit the bill...

Here's a link that might give you more insight, if you care to have it! :)

http://wcco.com/seenon/local_story_269232919.html

My hubby says maybe they're nervous and have to do something, but as far as he knows they chew because it helps them from getting too thirsty. Why such a big chew I have No idea. Take Care my friend...

I don't know why either.
But it does drive me crazy.
My oldest son is a huge sports fan and while he was growing up it was very hard to teach him how rude it is to spit in public or chew gum in a polite manner when the men he looked up to are so rude about it.
He is now 28 and somehow I got through to him, well at least about this issue. lol Susan

They chew on things to annoy the living life out of baseball fans watching at home while eating pizza, shrimp, fried chicken and a bacon chicken sandwich.
It also bothers me that baseball players chew gum or tobacco because this causes the players to perform even worse than before. Personally, the Milwaukee Brewers have played terribly for the past seven years. How do you hold down first place for so long and then get eliminated from the 2007 Playoffs two days before the end of the season ?

I guess they chew and spit for habit and because they are looking at a bunch of other men all the time. It might be rude but what you are looking at? Provocation and trying to get the other player off-balance is part of the game, right?