Question from Novice

Hey

I keep finding myself watching the games
on Channel 5 (UK)

I would like to know more about 'stumpings'
or what ever its correctly called when the ball gets
to the base before the runner

When running to first after a poor hit the batter is run out
pretty easily when the ball is thrown to the first base
when the catcher has a foot on the base. OUT

I have also seen during the games, and on films
where the baseman has to tag the runner with the ball ?

I also saw a play where the runner ran into the baseman
to make him drop the ball on purpose ?

Why the differences ??
Why run out with a foot on the base
and then with the tagging ?


TIA

M