Indeed they were. Above is one of the many friezes surrounding the "ball court" at Chitzen Itza. Just above and to the right of the turf is one of the "ball players" being decapitated while on bended knee. Above from the left corner of the turf is his head. It's speculated that the losing (or maybe the winning) team was dispatched right there on the field at the conclusion of the ball game as a sacrifice to the gods or the king or something else.
And this barbarity they PROUDLY depicted in stone! Imagine the horrors they didn't depict. Depsite wimps like Roger Friedman, many of us who yearn for no-holds-barred depictions of past civilizations will enjoy this film.
The Mayans recognized they were having inbreeding problems and so at the end of the game the loser's king had to give up one of his sons to the winner. That son (or stud) was then adopted by the winner king and made a prince.
But at some point a 200 year war commenced between the 1st and 2nd most powerful Mayan empires pretty much wiping out most of the people and resources. What was left moved north and started a new civilization that was much more violent.
I only know all this because I just got back from a trip through a few Mayan sites in the Yucatan peninsula with an archaeologist guide.