[washingtonismoney]

The Washington players were wearing some sort of halter around their chest with some cell-phone-sized box at the top of their spine on their back.  Since I don't think you're allowed to communicate that way to the players, I'm guessing it is some sort of instrumentation, either heart/respiration, position etc (but don't watch-sized sensors record that now) or maybe acceleration (concussion) measurements.  My best guess is that they're using cell phones to record position/speed so they can analyze it later.

Anyone know what it is?

Yeah, your instinct is correct -- they're probably sensors that record all sorts of physiological data. Here's one popular provider: http://www.catapultsports.com/

The problem with the wrist-sized sensors is they're of lower quality, generally.

[washingtonismoney]

The Washington players were wearing some sort of halter around their chest with some cell-phone-sized box at the top of their spine on their back.  Since I don't think you're allowed to communicate that way to the players, I'm guessing it is some sort of instrumentation, either heart/respiration, position etc (but don't watch-sized sensors record that now) or maybe acceleration (concussion) measurements.  My best guess is that they're using cell phones to record position/speed so they can analyze it later.

Anyone know what it is?

Yeah, your instinct is correct -- they're probably sensors that record all sorts of physiological data. Here's one popular provider: http://www.catapultsports.com/

The problem with the wrist-sized sensors is they're of lower quality, generally.