Just because something is marketed for guinea pigs, does not mean it is safe or appropriate for them. (Case in point those horrible balls) He obviously got cut from something. I would feel around everywhere and on everything to see if there is anything sharp sticking out. A vet visit might be in order if this was self inflicted from scratching - perhaps ear infection or ear mights? Now, you found these forums so you know about C&C cages. Hopefully, you will be making one as soon as possible so that your pig can run and play and get a buddy.
As far as neosporin goes, if it's anywhere that your pig could lick it (or wipe it with a foot and lick it off the foot) then it could make your pig very, very sick. Better to rinse or wipe wounds with dilute chlorohex solution or something like that. I hope it heals up ok, without any complications!