[1Old Pro]

two Soviet-era planes moving along the runway before one suddenly rams the tail of the other

next time check the brakes.

[RitchieAprile]

maybe it was a brake check. people do that all the time here
in WA.

[C210N]

Brakes don’t do much while the wings are still generating significant lift.

Looking at the vid, that looks like the case - still barreling down the runway at a good clip, aircraft weight still being held in the air, rather than bearing down on the wheels.