On the front page of Friday’s USA Today (yes, I go to the local market every morning to get a newspaper . . . on horseback) appears a story that could be very good news for football players.

And very bad news for the sport.

The Army has discovered a blood test that reveals mild traumatic brain injury or concussion, via the presence of “unique proteins that spill into the blood stream from damaged brain cells.”

“This is huge,” Gen. Peter Chiarelli, the Army vice chief of staff, told Gregg (hey, there’s another 3G out there) Zoroya of USA Today.

And indeed it is. If the test works, blood tests can be used to conclusively diagnose players who have had concussions — at every level of the sport.

Here’s the bad news. The test possibly could demonstrate a degree of mild brain injury that will cause parents throughout the country to prohibit their children from playing, cutting off the future supply of potential NFL players.

Factors that need to be addressed regarding the test include cost (especially at youth levels) and reliability. Dr. Jeffrey Bazarian, a trauma specialist, told Zoroya that the test has a possible flaw when it comes to being a conclusive detector of mild brain injury.

“The key is whatever patients they study need to look like concussed

patients, walking, talking and not necessarily in need of

hospitalization,” Bazarian said. “If you just look at the milds that are admitted . . . that’s potentially a flaw.”

Still, it’s progress toward better nailing down the inherently slippery question of whether a person has suffered a concussion — especially when the person is a football player who may be inclined to try to hide his symptoms so that he can still play.