Three 止 (foot) to indicate hurried movement. Originally the bottom part of 奔 (run), later written on its own as its variant. Modern component form is written as 卉 which standalone indicates an entirely different character, 卉 (grass). Not related to 牛 (cow).

Evolution

Seal script

Chu (Warring States: 475-221 BC)

Clerical script

Western Han dynasty (202 BC-9 AD)

Regular script

Modern