Adds a passive damage bonus to your attacks, and works better if you’re large and strong. Train this to a high level once you’re an expert at hitting with your chosen weapon and dodging the enemy.

The ingame help reads:

Skill duration: random.
Type of skill : neutral skill.
Affecting stats: St/Siz.
It uses no endurance points.
While size and strength generally makes one a better
fighter, it takes some skill in using that extra power
to its full effectiveness. Just being big doesn't mean you
are a good fighter, in fact many giants have been beaten
soundly by dwarves. It's not brute force that wins a fight,
but skill, the size and strength only helps a bit.