They did break the legs of crucified criminals so they'd die sooner ... seems like it would fit that they'd also finish off wounded gladiators.
ann
The only account of that is in the Bible and appears to have been a special case to hasten death before the Sabbath. Typically a crucified individual would take days to die, which is why this method of execution was reserved for rebels and those who really pissed off the Romans (odds are, the two "thieves" in the gospels were nothing of the sort because thieves were not crucified).