武 is indexed under the 止 (foot) radical, picking the four-stroke foot at the centre as the anchor. Classic compound-ideograph reading: a foot marching with a weapon - military action. The 止 sits inside the 弋 weapon-frame, picturing the soldier on the move.
A single horizontal cap at the top of the character, part of the 弋-frame that wraps around the 止 inside. It marks the upper limit of the weapon-bracket and helps establish the upper-left-corner enclosure pattern of the whole glyph.
The 弋 weapon-frame wraps around the 止 foot, with its upper stroke coming first and the slanted body plus dot finishing the character. It supplies the 'weapon, military force' half of the compound, balancing the marching foot inside.
