If a fallow buck is down during the rut, the other bucks will gang up and kill it. Especially if it is a dominant buck. For example a buck which has fought a fence and become entangled, is defenceless. Other bucks will very quickly come and stab it with their antlers or spikes. The spikers are very dangerous.

That wapiti bull looks like another bull has had a go at it while lying on the ground.