I think perhaps a minimum speed rule, make it across the arena (longest distance) in 30 seconds. If you can't traverse the arena in 1/6th of the total time of the fight then you are not in the fight anyway.
By having a set distance and time you can have black and white decisions, at the end of the fight if you contest the decision of the judges on immobility. You can attempt to complete this test if you pass your not immobile, if you fail you are.
Giro movement, if your weapon gives you this option good on you. if you pass the test you are mobile.