What are the dos and don'ts of positioning your thumb on a guitar?

If you consider the purpose of the thumb to be to counteract the pressure of the fingers, then the ideal placement (for playing a chord) would be directly opposite the "center of gravity" of the polygon formed by the fingertips.

But this ideal may be difficult to achieve depending on the length of the strap. I set my strap quite short so the guitar is positioned rather high against my chest; this (for me) seems to help the thumb to naturally rest in an appropriate place.

For a moving line, I try to keep my thumb opposite the middle finger. For a barre, it should be opposite the finger performing the barre.

All of the above is intended to put the least amount of stress possible on the delicate tendons in the wrist.

Source: http://music.stackexchange.com/questions/8347/what-are-the-dos-and-donts-of-positioning-your-thumb-on-a-guitar

adam shulman peanut butter recall jason aldean Brigitte Nielsen Cricinfo Geno Smith ny giants