Skin Problems Scabs on guinea pig- bites or mites?

First, mites don't cause wounds themselves -- they're invisible, and they burrow under the skin and make the pig itch. If a pig has a really bad mites infestation and is scratching and biting at itself a lot, it can injure its own skin. But if that's the case, you'd be aware of the massive scratching, and there would be patchy hair loss as well.

It sounds like your two pigs have gotten into a squabble. That's common at that age, as the teenage hormones are raging and they're trying to establish who is the dominant pig. It can be exacerbated by a cage that's too small and/or too crowded, hideys that have only one entrance, not enough water bottles/pellet dishes/food bowls, etc.

Click on the Main tab at the top of this page for cage size recommendations, and remember that bigger is always better, especially with boars.