Continuity mistake: At the airbase when Mike is walking from his room into Marcus' to show him the horses on his laptop he's carrying a banana, however in the room he has an apple in his hand. (00:09:00 - 00:10:00)
Continuity mistake: In the scene where Marcus is removing the shrapnel from his leg, when he gets to the last and largest piece, he places the medallion from his necklace in his mouth to bite down on. As the scene transitions from the leg to his face as it is removed, he appears to no longer have the medallion in his mouth. Then once the shrapnel is removed, he collapses and still has the medallion in his mouth.
Continuity mistake: When the helicopters are coming to save Lutrell, the sky is blue with no clouds, but the view from the plane providing cover fire shows heavy cloud cover.
Continuity mistake: Throughout the movie, the viewer sees multiple shots of the SEALs firing at the Taliban, then the shot zooms in to a through-the-rifle-sight shot. In several of these shots, the SEALs are quite obviously canting their weapons to the left or right, yet when the shot zooms into the sight, the crosshairs are perfectly level. They should be canted, too, if the rifle is canted while firing.
Continuity mistake: In the final shoot out when the Taliban bad guy is coming up on the guy that saves Mark Wahlberg, there is a bullet wound on the back of the brown vest (top left, back left shoulder), but a few minutes later when he wrestles the Taliban leader that wound or blood stain isn't there.
Continuity mistake: When the seal team are watching Taliban with binoculars in the village below, the range finder changes significantly when binoculars are passed from one member to another or Taliban are viewed again.
Answer: SEALs are allowed to have 'modified grooming standards'. They are often undercover in other countries and it helps them to blend in, as beards are far more common in the Middle East.
Grumpy Scot