Sam B has this skill under the Combat tree. The lowest level you can get this at is level 5. The Ram enemy does not appear until Act 2. They are the bigger enemies in straight jackets. Your best bet against the Ram will be to dodge his initial attack and let him run into a building or something, then whack away at him until he's very low on health. From there, use a few tackles to finish him off. The skill doesn't do too much damage though, and you'll still have to hit him in the weak spot in the back so it can take quite a few hits. Upgrade this skill to level 3 for best results