As I understand it, he was helping clear snow from neighbors' driveways and he got out of his snow plow to help someone (a family member?). He was injured when he tried to get back into his snow plow.
He's been sharing updates with his fans from the hospital. Here's a recent one.
Jeremy Renner posts video update: 'ICU spa moment to lift my spirits' | CNN
I meant to say something the other day but it's been a busy week for me.