In
World War I, going over the top was when soldiers crawled out of the
trench and ran through
no man's land while being
cut down by
machine guns hoping to get enough people to the enemy trench to take it, thereby gaining
territory.
Now, "over the top" is an
idiom that indicates
excessiveness. Personally, I think that what distinguishes something that's over the top from something that's merely excessive is that being over the top is to be
gleefully excessive. It's a
silly excessiveness that, when applied to
violence, has elements of
black humor. Violent scenes in
The Matrix tended to be over the top, but not the ones in
Braveheart.