catch, arrest
拏 centers on seizing or taking hold of someone or something, especially in a forceful or legal sense: catching or arresting.
拏 combines 奴 (which may contribute a phonetic element) with 手 (hand), suggesting the action of grabbing or seizing with the hand. The exact historical development is uncertain.
The top part 奴 can be thought of as a person being subdued, and the bottom 手 is a hand. Picture a hand grabbing a person to catch or arrest them.
For ダ, imagine a hand catching a dart out of the air: dart -> ダ, and the hand seizes it firmly.