roll into a ball, slap
摶 centers on shaping something by hand into a compact form: rolling into a ball, or delivering a quick, rounded strike like a slap.
摶 combines 扌 (hand) with 專, which likely contributes the sound and the idea of concentrating or rolling something together. The exact historical development is uncertain.
The hand 扌 beside 專 suggests a hand working something into a concentrated shape: rolling dough into a ball, or cupping the hand to deliver a rounded slap.
For タン, imagine rolling clay into a tan-colored ball: tan -> タン, and your hand shapes it.