It was pretty hard to take light measure on this one. It was shot on an Hasselblad 500 cm which has no internal light meter, and even with an external light meter it would have been impossible to take light measure. So I thought hard and guesses it: f/4, 1/500s @400 ASA.
It turned out well!
What an amazing moment you captured there. Snapped in just the right moment.
@runicar thanks a lot!