I think everyone here has read a bit
too much power fantasy. This isn't a situation where, once exhausted you can even kill the gorilla. How do you propose the men kill the gorilla? They can, at most, blind it. Our teeth can maybe
MAYBE do some damage to their muscles. That'd be the humans only chance, to repeatedly bite the gorilla. Throwing rocks won't be enough, the gorillas are too muscular for more than bruising. The average man would very likely never even think to bite it. How many men die before they figure it out? Most men would try to punch, kick, or throw stuff at it. This is just a massacre of men. This question is like asking how many men does it take to fight a ford f-150 and win. Sure, eventually the tank runs out and they can dismantle it, but 100 men isn't enough.
The strategy would be to cling onto the gorilla to slow it down as the others attack it. It will be bloody, but 100-1 is too much of a difference.
You can fit 4, maybe 5 men on the back of the gorilla if you're pushing it. If they're the average man as described, they're 90kg. Sure, half of what the gorilla can carry. Issue for those men is that gorillas can easily grab things on their back, and swing them THROUGH other attacking men like a club.
Silverbacks only become silverbacks by fighting other gorillas in combat repeatedly. These are battle hardened gorillas that fight and win against other gorillas. They know how to fight and how to kill. Further, the 800kg estimate I gave is on the low end for them, that's a weak silverback. Peak silverback bench press strength is like 1800 kg. So, we can put the average at like 1300kg.
Exhaustion is only a factor if the fight is strenuous. Lifting a human man and spinning him around isn't a strenuous activity for a gorilla any more than carrying two grocery bags is for a weightlifter. It's a massacre of men.
For an idea of exactly how one sided this is, this is a chimpanzee getting it's hands on a raccoon. The numbers work out such that the approximate weight and strength is about the same as a human and gorilla. You think 100 raccoons would be able to beat a chimp?