The Pocket: within a music groove, the obviousness and follow-ability of the “main” beat. If the rhythm section has set up a groove everyone can follow, they are said to “have a great pocket.” The music equivalent of “throwing a catchable ball.”
The Rolling Stones wobbly Pocket: The Stones famously have a hit-or-miss relationship with a groove. When they are on, there are few better. When they are off…you notice.
Here’s their first song on the Scorsese live doc Shine a Light - they open iwth Jumpin’ Jack Flash: - YouTube
That’s a bit of a hot mess, eh?
What happens when the pocket wobbles? Typically, it is Keith thinking he is “haiku Ray Charles.” Unlike most bands, Charlie the drummer keys off Keith, not the bassist. (Hetfield does this with Ulrich, too, in Metallica). If Keith is establishing a strong groove and holding it down, every follows along. But if he tries to do something cute, it can fall apart. I believe that Charlie is following Keith to establish the groove for that performance, but Keith wants to do something flash before Charlie has fully picked up the cue, so he is still hesitating behind Keith. And…a mess for a bit.
In that clip above, Keith is starting off trying to be all macho, and tries to add a bit of flash. Around 11 seconds in, he drags the beat - a small version of Ray Charles holding back on the second “America” the way only he can - and then hits that open chord and pops his pick hand out. He’s flourishing - but now the groove is incoherent. So when Ron Wood’s lead bit pops in, it sounds a bit random.
After than, Keith is throwing expressionist chord jabs in a few random spots - it takes a good minute into the song before you start to really get a solid JJF feel. But again, around 1:30, Keith hits a random chord. Dude. You’ve impressed Scorsese; please establish the groove the way only you can.
It was worse when Bill Wyman was in the band, because he would play a bit ahead of the beat (I have a theory that Wyman was a bit butt-hurt that Charlie liked Keith better, so Bill would try to anticipate the beat as a way to trying to show he could drive it, too!! ;)). If Bill came in ahead, Keith dragged, and Charlie then followed Keith, it could get ugly.
Other musicians have thoughts on the Stones’ and their wobbly pocket?