Shields in BatMUD are considered weapons, and you’ll attempt to bash enemies when you have one equipped. This skill improves the damage you do with such attacks. Most players only use shields when they’re defending other players in a party, but there are a few shields that do reasonably high damage.

The ingame help reads:

Skill duration: random.
Type of skill : neutral skill.
Party rows    : 1st.
Affecting stats: Str/Dex.
It uses no endurance points.
While shields are usually used for protective purposes,
they can also be used as weapons. By fooling your opponent
into thinking that you are hiding behind the shield, you can
catch him off-balance. Many skilled fighters can use their
shield to knock their foes to the ground. Some shields are
light enough that you can actually swing them, using them as
a bludgeon. The more common approach is to use your weight
and push the shield into the opponent, knocking him to the
ground if possible.