Frenzy Boar

Frenzy Boar is a low level monster that can be found on the field of SAO first floor beyond the Starting City. It is the weakest of all enemy monsters and can be killed easily with one precise blow, although it must first be provoked by the player for it to attack.

Sword Art Online
When Klein first met Kirito, he begged him to show him the basics of SAO, so Kirito took him outside to the starting fields and taught him the attack basics by fighting these creatures.