This is something that is still being debated in academia. I tend to lean on the side that no one was actually sacrificed, but instead the imagery we see in ballcourts or on murals or painted on ceramics does not necessarily represent actual events taking place (at least in the case of the Maya). Instead this imagery of the ballgame and someone being sacrificed is tied into the Hero Twin myth made popular by the Popol Vuh and later backed by the Bonampak murals as being a central myth to Maya mythology and religion. In the Hero Twin myth, the father of the Hero Twins, as well as his twin brother, challenges the gods of the underworld to a ballgame. They end up losing and the father is beheaded. It is only later, after his head has sprouted into a tree, that he spits into the hand of a young woman who becomes impregnated with the Hero Twins. After being raised by their mother and grandmother, the Twins set out to restore their father's head to his body. There is explicit imagery that ties the ballgame ball with severed heads, sometimes using the actual head as a ball.
I highly suggest reading the following book which discusses the ball game iconography as well as other sacrifice in Mesoamerica.