This is a hamstring PAIL/RAIL stretch to help improve your hip flexion and reduce compensation through the lower back. Proper hip mobility is crucial for a consistent and efficient golf swing.

1-2 minute stretch - deep diaphragm breathing into the back of the leg (hamstring) complete relax and don't hold on to tension.
10s + PAILs contraction - slowly ramping (20%, 40%, 60%) up a contraction in the tissue we are stretching (hamstrings, back of the leg)
10s + RAILs contraction - slowly ramping (20%, 40%, 60%) up a contraction in the opposite tissue (quad, front of the leg)
** after releasing the RAIL contraction you should gain 15 degrees of range, you can hold in this new range and repeat the process:

Caution: if you are new to PAILs and RAILs contractions start at 20 or 40% and and work on your stretches 5 days a week, once you have the feel and have increased you tolerance you can increase the contraction 60%+ and reduce your days to 3 days/week.