<wielded> a practice polearm
You need to wield a staff or spear to leg sweep.

'LEG SWEEP' LEGSWEEP
syntax: legsweep
legsweep <victim>

With the long shafted weapons (spears, polearms, and staves), a sweeping
strike at the opponent's legs can knock them down to the ground. Flying
opponents are immune to this. This technique may be used to initiate combat.

To leg sweep with a polearm, you need to be specialized in it.

So long, and thanks for all the fish!