How many different ways...?

There are many

With a runner on base and the pitcher on or astride the rubber, it is a balk when the pitcher:

-switches his pitching stance from the windup position to the set position (or vice versa) without properly disengaging the rubber;

-when going from the stretch to the set position, fails to make a complete stop with his hands together before beginning to pitch;

-throws from the rubber to a base without stepping toward (gaining distance in the direction of) that base;

-throws from the rubber to a base where there is no runner and no possibility of a play;

-steps or feints from the rubber to first base without completing the throw;

-pitches a quick return pitch, that is, pitches with the intent to catch the batter off-guard;

-pitches or mimics a part of his pitching motion while not in contact with the rubber;

-drops the ball while on the rubber;

-after a feint or throw to a base from the rubber, fails to disengage the rubber before reengaging and pitching;

-after beginning to pitch, interrupts his pitching motion;

-begins to pitch while the catcher is out of the catcher's box when giving an intentional walk;

-while pitching, removes his pivot foot from the pitching rubber, except to pivot or as a natural consequence of stepping forward to release the pitch;

-unnecessarily delays the game;

-pitches while facing away from the batter;

-after bringing his hands together on the rubber or engaging the rubber with his hands together, separates them except in making a pitch or a throw;

-stands on or astride the rubber without the ball, or mimics a pitch without the ball; or

steps to first base and throws to the first baseman who, because of his distance from the base, is (or would have been) unable to try a tag against the runner at first base

-In addition, if a pitcher commits any of the following illegal actions, it may result in a balk under certain circumstances:

-expectorates (spits) on the ball, either hand or his glove;

-rubs the ball on his glove, person or clothing;

-applies a foreign substance of any kind to the ball;

-defaces the ball in any manner; or

-delivers a ball altered in a manner described above or what is called the “spit” ball, “shine” ball, “mud” ball or “emery” ball.

Also, he can balk when the the pitcher is holding a runner on first and when he goes into the stretch position. If when he looks over his shoulder but turns his shoulder without breaking his hands and stepping off the mound. This is once he is actually in the stretch right before he throws.

1. By putting their foot behind the rubber without throwing home..

The only way.. Say if they're trying to throw someone out and they wind up and their foot goes behind the rubber on the mound it's a balk.. But if they wind-up and their foot stays on the home plate side of the rubber and they throw to first it's legal.

Hope this helps.