Crossing legs for a while causing numbness, is it due to ischemia to the nerve? or to the vascular structures that cause numbness?

Peroneal : The peroneal nerve gets compressed at the lateral fibular area, and in part the small vessels, vasa nervorum get compressed, with some mild localized and reversible ischemia, but also transient axonal transport cut-off with less distal nutrient delivery. But the nerves cause the numbness, not the blood vessels.

Nerve: Compression is more likely in your age group If Vascular cause there will be more pain first