Can I hurdle a defender?

No. Hurdling is an illegal personal contact foul. For 2026-27 it's defined for the first time (Rule 2-18): an attempt by a player to jump (hurdle) with one or both feet or knees foremost over an opponent who is touching the ground with nothing but one or both feet.

In other words, you can't leap feet- or knees-first over a defender who is standing up.