You may remember how advancement works in the arena. 3 wins advances you to the next level, and all fights are to the death. So if you advance from Pit Dog to Brawler it means 3 people had to die. To advance from Brawler to Bloodletter a combatant must kill 3 more people, but remember that combatants only fight others of the same rank, so to get to bloodletter requires the death of at a bare minimum 9 competitors (3 brawlers with 3 kills each), and this is assuming that each combatant has the minimum kills required to enter each rank.
And there are 7 ranks plus a champion.
Each Hero rank combatant required the death of at the very least 2187 participants, and there are at very least 3 heroes and one champion (requiring 6561 deaths minimum) on the yellow team. Again, this is assuming ideal progression.
Since matches between high rank combatants seem to happen fairly often (you can get a match set up whenever you want), I think we're looking at a wholesale slaughter on the scale of hundreds of thousands or millions per year.