A tussle is a rowdy fight. If the rambunctious kids you're babysitting get into a tussle, you may have to separate them for a while and calm them down.
Though a tussle is often a physical fight, it's rarely a serious one. Two wrestling dogs, a couple of scuffling teenagers — these are examples of tussles. The word tussle is Scottish, a variant of touselen, which is related to tousle, or "dishevel or muss," which you might do to a little kid's hair. The root of both is the Old English tousen, "handle or push about roughly."