The etymology of 競 is very complicated, or else Henshall has presented it unclearly. I’m not sure which.
The part at the bottom (儿) usually means “legs.” But according to Henshall and one other source, each 儿 represents a person here. These two people are adversaries involved in a dispute.
Meanwhile, Henshall says that the remaining, upper parts evolved from an old Chinese character that meant “to argue.” But another source says that the whole of 競 originally meant “to argue.”
So perhaps 競 represents Henshall and that other source as they duke it out over the etymology!