Assuming Felix is still one of the spearmen in this panel, rather than the guy in the bear skin, his wounding works like this. Felix's comrade warns him of spearmen coming up behind, He spins around to his left in order to get the shield in place as quickly as possible (spinning right would engage his sword faster, but would leave him vulnerable to attack substantially longer) An enemy spear strikes him in the back as he's turning, as it pierces his mail and plunges into the underlying padding, then Felix's shield knocks the spearpoint aside. So it takes a gouge out of back muscles but doesn't go as far as vital organs or damage the spine. There's probably a cracked rib or two though. He should be able to recover from that, but will have a dandy scar. So what happens when the spear point skids past? Well Felix probably continues to turn, and sorta corkscrews into the ground... his shield-companion catches him before he totally collapses, I think. That explains the next panel where the buddy is supporting him.
So is that workable for you? Just my opinion, of course. (PS, it appears the term 'buddy' comes from butties... companions who shot at the same archery butt. So shootin' buddies go back at least as far as the middle ages. Ain't language cool?
DRW
DRW.