Phew!
Boxing isn't slow.
Just because something is immensely powerful doesn't mean it's slow; it just lacks agility.
Jack threw a straight punch, and once his punch was in motion, it was very difficult to alter its course. He thought this punch would once again force the enemy to retreat, but things were different this time—
In the Hot Sight, two exceptionally red figures advanced instead of retreating!
As a human, one's understanding of "movement" in combat is also based on one's own fighting experience.
Jack was an experienced boxer, good at fighting with wide, sweeping movements. He had seen many agile and flexible opponents, but this was different.
In the milliseconds of his punch, the two enemies' bodies bent forward in an inhuman manner!