Re: How is rosin used, where does it come from how does a basball player use it

Talcum powder, chalk, resin (powdered glue), rosin, and other powders are
used to provide better (drier) grip  while reducing the chance blistering.

They all work in different ways.
 
Some powders absorb moisture (like talc and chalk) so that the grip is
based on strength of hold not skin friction against the object being held.

Resin is usually applied to the object to be held -- like a baseball bat
or an axe to reduce the chance of the object slipping.  Rosin is usually
sticky combination of chalk or talc and resin.  It is sort like the post-it
note of powders.  It will stick slightly, but if pulled only slightly will
let go.

Rosin is most often associated with baseball pitchers and bowlers.  In bowling,
it provides a good non-slip grip on the bowling ball without transfering
substance to the ball.

What rosin does for a baseball pitcher is not very straight forward.  Some
people claim it is a mental crutch that pitchers have.  Its existence stems
from a time when only a few baseballs were used in a game.  A baseball will
become more slick with more use.  Rosin helps a pitcher dry off his hand in
a controlled way -- who knows what sort of gunk (illegal substance) will be
a pitcher's hand if he wipes his pitching hand on his uniform.  Rosin also
has a slight tackiness to it, so that the ball will stick to a pitcher's
hand better if he desires.  If the ball sticks better to the pitcher's hand
then he may be able to produce more spin on the ball when throwing a curve
or a  slider.

The following is an excerpt from the Major League Rule book section 8.02e
under the rules 8.00 Pitchers and 8.02 things a pitcher cannot do. 
-----------------------
            (e) The umpire shall be sole judge on whether any portion of
 this rule has been violated. All umpires shall carry with them one
 official rosin bag. The umpire in chief is responsible for placing the
 rosin bag on the ground back of the pitcher's plate. If at any time the
 ball hits the rosin bag it is in play. In the case of rain or wet field,
the
 umpire may instruct the pitcher to carry the rosin bag in his hip
 pocket. A pitcher may use the rosin bag for the purpose of applying
 rosin to his bare hand or hands. Neither the pitcher nor any other
 player shall dust the ball with the rosin bag; neither shall the pitcher
 nor any other player be permitted to apply rosin from the bag to his
 glove or dust any part of his uniform with the rosin bag.
-----------------------

I hope this helps.

Tom "Gaylord Perry" Cull