Goofs

When Isaac is hiding against the wall, there are obvious tally marks on the wall behind. A few moments later, he makes those tally marks.

When they're counting the bodies early in the movie, the dead body inside the vehicle is sitting upright at the beginning of the shot. As the spotter pans away toward the third body, the body in the vehicle now has his head resting on the steering wheel.

When Isaac crawls back behind the wall after collecting the radio from the dead marine, the wall with the door opening is completely demolished by the sniper. A moment later the door opening is mysteriously back again.

During a scene where the main character is overhearing radio chatter, some one says "over and out" which is incorrect radio procedure. "Over" means "my message is finished and I am waiting for your reply." "Out" means "I have finished talking to you and don't expect a reply." One would never say "over and out"; one would either say "over" to continue a conversation or "out" to end it. Any military personnel allowed on a radio would know this.

Early in the movie, when Issac is removing blocks from the wall to make an opening to look through with his scope, the blocks fall and damage his hand, specifically his right index, or "trigger finger". That finger is shown bloody and misshapen, possibly broken, for a vast majority of the remainder of the movie. At the end, he is able to take a shot at the enemy sniper using that same finger and it is shown to be uninjured. Precise trigger control is critically important to making accurate shots, particularly for a sniper. Making a long range shot like that with an injured or broken finger is highly unlikely.

The enemy sniper, Juba, could target Matthews and Isaac easily and communicate over military frequency on the radio.

At around 12 minutes and 10 seconds into the movie, after taking initial fire from the sniper, Isaac calls out for John Cena's character, Staff Sergeant Shane Matthews, but mistakenly calls out "John".