Actually, it's real techniques twisted to look Shounen-y. There is a panel that implies Sena took a quick step back, juked Yamato, then burst forward. It strains the back leg due to the cut and turn, but it's possible. The whole "time travel" shit is actually just Yamato's mind reeling from the quick cut.

"Sweetness" Walter Payton was famous for doing things like that. Sena is modeled after Sweetness. Some people that have played against Sweetness have joked that they saw a ghost whenever he had the ball.

Everything in Eyeshield 21 regarding the game itself is real. They just made it look like a shounen sports manga instead of drawing it straight up.

Granted, it just means Sena is special as f*** since in real football there hasn't been a guy like Walter Payton in a long time.