Researchers say the repetitive moments of blocking and tackling plus the weight of helmets and pads can take off nearly 1/2 inch in height off players.
The defensive high impact actions compresses the spinal cord.

No surprise. Anytime you repeatedly compress the spine like they do, it's bound to happen. It's the price for playing the game.

If I would have thought about it I wouldn't have been surprised. But it sounds weird when you say playing football makes you shorter.