I noticed when i'm tired around 15-18 holes, when I do the lagging club take a way I could feel the club running out of my left hand. The butt of the club sort of just pops out from my left heel pad. Usually i start hitting 10-20 yards push when that happens. Am I not gripping hard enough?
If you end up getting to close to the ball and get in a bad posture by bending from your shoulders and not your hips that can happen and usually a shank is in the making. Tired or not you should implement a preshot routine which covers all the basic setups especially grip and posture and maybe a swing thought that gets you a good takeaway that starts club and body properlly. It also helps to take water frequently and a energy bar to keep your stamina up.
If you don't exercise start a program. Golf is a physical game.
Finally be very observant when you see the problem and make some variations and try practice swings with and without changes (grip,posture ,distance from ball) till you can create the problem and then fix it making the change that eliminates the problem.
You can do this as well right in your house by experimenting and what happens when you make some of the variations I mentioned,
I had this problem myself and I found that i did not have grip right and this forced my hands to turn on the takaway and pull my right hand off the club. I tried everything like interlock and other grips including grip pressure but it did not help in fact in made it worse. I then got a pratice grip and memorized every position it put my hands in and I found I could hold the club with very little grip pressure. Improvement in plane, club head speed and a better pivot were dramatic.
The mistake I tended to make was not getting my right fingers in the right hand properly and not having my lifeline properly covering the left thumb.
Good Luck in finding your problem and please let me know if you find the problem.
by the way if you interlock don't go to deep with finger or you will get the club in your right palm which does not work for me or many others.
Dave