Sand pit workouts are THE WORST. Jumping that high while changing direction that quickly, on sand? Forget it. (Related: Beach volleyball players are way tougher than you think.)
The video comes from OBJ's trainer, Jamal Liggin, who is based in Hollywood, California. Visit his website and you'll see that a barefooted Beckham running on sand, often against resistance, is a recurring theme. The Giants receiver does resisted speedwork in-season too, but Liggin appears to have mercy on him then, asking him to do it on a floor rather than on the beach. Workouts on Liggin's Instagram page look similarly tough, with some especially brutal pool work.
If you think OBJ might be neglecting his strength work, rest assured he's getting his swole' on too. Beckham's Instagram page shows him performing explosive lifts and rotational strength moves like the Med Ball Core Rotations.