Quick answer: On video, the putting backswing is long and the putter head slows down into the ball; the follow-through is shorter than the backswing.
What it does to the ball
Putts that die before the hole and wobble off line: a ball without speed obeys every imperfection in the green.
Root causes (by frequency)
A backswing too long for the distance
Fear of racing it past on fast greens
How to fix it
Short backswing and smooth acceleration: follow-through always equal to or longer than the backswing, and the ball 30-40 cm past the hole if it misses
Drills that fix it
Always past the hole · 10 min · 20 reps
Eradicate deceleration and putts left short A series of 2-4 m putts with one rule: every ball that doesn't drop must finish 30-50 cm past the hole. Shorten the backswing and accelerate smoothly. Ten putts in a row obeying the rule to end the session.
Frequently asked questions
What is "Deceleration in the putting stroke" in the golf swing?
On video, the putting backswing is long and the putter head slows down into the ball; the follow-through is shorter than the backswing.
What does deceleration in the putting stroke do to the ball?
Putts that die before the hole and wobble off line: a ball without speed obeys every imperfection in the green.
How do you fix deceleration in the putting stroke?
Short backswing and smooth acceleration: follow-through always equal to or longer than the backswing, and the ball 30-40 cm past the hole if it misses
Sources
Dave Pelz — Dave Pelz's Short Game Bible
Dave Stockton (con Matthew Rudy) — Unconscious Putting