Retirement Pastels

Theme:  Head Over Heels or Tumbling.
Here is today's theme song.
This theme is unusual. Instead of the meanings of theme fill words, it's based on the placement and repetition of a certain syllable within longer words in the grid.  That syllable is "END, " which is also a word meaning the extreme part of something...

Theme:  Triple doubles.  Each theme fill contains three groups of doubled [or more] letters.
First, the unifier --  58 A. Impressive basketball feats, and what 20-, 36-, and 43-Across have: TRIPLE DOUBLES.  A triple-double in basketball occurs when a player achieves double digits (10 or more) in three of the five main statistical categories...

Theme:  The POT has me running in circles.
17. Like some fast planes: JET POWERED.   Refers to a vehicle or device that is propelled by a jet engine, which creates thrust by expelling a fast-moving jet of gas. While most commonly associated with high-speed aircraft, this principle is also used...

Theme: Finger Noises.  Each multi-word theme fill contains an example of one.
17 A. "Turn that frown upside down": CRACK A SMILE.    To begin to smile, or to smile slightly, often unexpectedly. It implies a subtle or brief smile.  One can also CRACK one's knuckles....