The trapezius is a large muscle that spans the neck, shoulders and back. Its chief action is to support the shoulders and limbs and rotation of the scapula necessary to raise the arms above shoulder level, which explains why the most discomfort is coming when Davis tries to throw.
It is not immediately known how serious the injury is or if it will require a trip to the disabled list, but Davis has had previous issues in the area. Davis had a right shoulder strain last season that caused him to miss about three weeks.
The 26-year-old is hitting .274 with 14 homers and 40 RBIs in 70 games for the Orioles this season, and is 4-for-12 with a double, a homer, two runs scored and five RBIs in three games this road trip.