Hmong broken, bruised, cracked, and otherwise screwed my ribs up many many times I can say it's probably the second most painful injury I've had. (Tailbone being the first and damn does that hurt). Don't forget if he's on the ground he's likely going to curl in on himself both for protection and from pain.
I'll divide it between the top ribs (ribs 1-7, also have heard then referred to as the 'true ribs') and bottom ribs (ribs 8-12, also heard them referred to as the 'false ribs'. You know you spend to much time in the tender care of the emergency department when you start picking up on the medical terminology), though I'll sometimes refer to the floating ribs separately (those would be ribs 11/12) and in some cases distinguish between left and right sides of the rib cage. Keep in mind my medical knowledge is limited to listening to the docs grumble and experience watching them put me back together again. I don't know technical terms beyond some of the injuries I get which happen a little to often. Now I'm assuming this is an injury caused by blunt force trauma via a fist or foot rather then say some of the more creative ways of trying to murder your ribs cage. Also assuming you've missed damage to the actual organs. Keep in mind I have an incredible amount of pain tolerance. Put it this way, the nurses are no longer allowed to ask how much on a scale of 1-10 in order to figure out if I really need pain meds because my 3-4 is about other people's 12-'I'm in too much pain to count any higher' levels.
bruised ribs:
Top left- every movement is going to be painful. Breathing is painful, thinking about breathing is painful, muscle swelling and surrounding tissue swelling can really screw with internal organs. Best treatment I've found is a hot compress while laying on my non injuries side and wishing I was dead so I didn't have to feel pain anymore.
top right- pretty much the same deal, slightly less painful I find because you don't have to worry about that annoying muscle called the heart beating.
Either side you aren't going to be doing much heavy anything for a while without everything being painful. You probably could lift heavy objects but you would be in so much pain the next day after your body slept that you wouldn't be getting out of bed without assistance.
bottom ribs- hurt like hell but I could mostly ignore them. Was still able to ride, lift hay bales and buckets. Couldn't carry my backpack on my back though, stretched things that didn't need stretching.
fractured:
top- depending on how bad the fracture is, continuing to work especially if you do any kind of lifting or swinging creates a much higher chance of further damaging the ribs. If they are badly fractured it could cause them to go snap crackle pop in ways the body is never meant to do. In this case, (at least the two times I did it) rather then the ribs snapping in from the force of a blow, mine snapped outwards and not very much (in actual movement wise.) but I most certainly felt it (although that could have been the internal bleeding as my rib clipping some blood carrying vessel which was apparently important enough to warrant interesting reactions. Maybe because I was breathing out as I lowered one end of a trough of water in one case and the other dropping a sack of grain they snapped in weird ways. I would suppose if you were bent over to lift something it would snap inward as you generally inhale when lifting so your rib cage would be constricting.
bottom ribs- painful, you won't be doing much of anything. Kinda like being kicked in the balls I imagine but without the pain fading after awhile.
floating ribs- if it requires movement it's going to feel like someone forgot a sharp surgical instrument inside you after try cracked your rib cage like an egg. Just saying. Honestly fractured floaters hurt not then some of the breaks I've had.
broken:
now everytime I've broken my ribs I seem to get some kind of infection in the lungs. Though that could be my body loosing all faith in my ability to keep out of trouble.
Top (1-3)- honestly not that bad, at least for me. Most of the time I can get through the pain easily enough if the break isn't really that bad as breaks go. I usually show up in emerge either because of my lungs being infected (pneumonia sucks) or because of bleeding.
Top (4-7)- New levels of pain. Basically reached curl up in a ball and hope to die levels of pain. You are not doing anything else other then maybe reflexively trying to punch the wall (as opposed to the doctor) when they play poke and prod. You can work through it if you have a high pain tolerance but you risk further damage that would then have to be surgically corrected. On one memorable (and by memorable I mean mildly horrifying) occasion I had clipped a blood vessel that was apparently important in some way and blood started filling up between the ribs and lungs compressing them. I was fine for a while before I realized that breathing should be painful not increasingly difficult.
Bottom (8-10)- meh, not that bad unless you're still breathing. Yeah that breathing thing? Every time your rib cage expands and contracts it's going to send shooting pain through your body like a little kid jabbing a bad bruise with their finger as you get tased.
Floating ribs (11/12)- can't honestly say, mine were surgically removed after is broke them in such a way that they decided to migrate to other places. Mind this was after I had broken them a few times previously and so they weren't in the best of shape to begin with.