to weigh, cut, come without being invited
敠 centers on the idea of measuring or judging weight, which extends to cutting or trimming to adjust weight, and figuratively to arriving or intruding without being weighed or invited.
敠 is a rare character. The left component 叕 is obscure and its role is uncertain; the right component 攴 (strike, action) suggests an action-related meaning. The exact historical development is unclear.
The left side 叕 looks like a hand holding a measuring tool, and the right side 攴 suggests an action. Imagine weighing something by hand and then cutting it to adjust the weight.
For タツ, imagine a tats (a made-up unit of weight) being measured on a scale: tats -> タツ, and the hand strikes to cut the excess.