Famine. I’ll defer to you. :)
I guess when who and where. I read a story about a man who was supposed to be a gladiator in some fashion. I remember that he was short in stature, 5 ft tall, and had several broken bones that had healed. He was a strong individual based on his frame — larger bones and short, I guess. A nasty person if you ever met him in an alley.
They were able to look at his teeth and conclude that he had several periods in his life where food was in limited supply. Especially while he was a child. They implied and even mentioned that this was common.
It was insensitive of me to ignore the plight of Roman slaves, they led pretty hard lives. OTOH, sometimes slavery was entered into willingly by someone with special skills but had fallen onto very hard times. Gladiators were mostly lowest of the low, but from time to time someone from genteel society (including the emperor Commodus, who was rumored to be the bastard son of a famous gladiator of an earlier generation) would enter the arena, which meant becoming a slave, in the hope of hitting the bigtime in Rome, and making a massive fortune, then retiring before losing and getting killed, or getting permanently crippled.