Your hips leave the bench as you drive the bar up, usually on the heaviest reps of a set.
Drive your feet into the floor and back toward your head, not down
Leg drive should push you into the bench and up toward the bar, not lift you off the seat.
Pull your feet back closer to your hips
Then get them flat and wide enough to feel stable.
Keep your glutes in contact and squeeze them through the rep
Actively cue contact rather than assuming it.
Reduce the load until you can hold the position
If your hips leave the bench, the rep would not count in competition anyway.
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