Keep elbows in so the putter head can lever and release
The coach explains that the elbows are the pivot points that let the claws work around them and control how the putter head lags and releases. With elbows kept in, the head works back behind the handle and releases forward of it through the stroke; with elbows out, the handle and face move as one, the head does not lever back, the clubhead goes first through impact, and face control and roll are lost.
Channel: stayhandsy
Watch official source at 2:30