obstruct, impede, bar, hinder
攔 centers on blocking or stopping movement: obstructing a path, impeding progress, or hindering an action. The idea of a physical barrier extends naturally to any kind of obstruction.
攔 combines 扌 (hand) with 闌, which likely contributes the sound ラン and the idea of a barrier or obstruction. The exact historical development of 闌 is uncertain, but the character as a whole suggests using the hand to block or hinder.
The left hand 扌 is placed beside 闌, which looks like a gate or barrier. Picture a hand pushing against a gate to obstruct passage.
For ラン, imagine a runner being blocked by a hand: the runner's path is obstructed, and 'run' cues ラン.