A bicyclist was seriously injured Sunday on one of the area’s most popular bike trails when another cyclist reached out and struck him as they passed each other, authorities said.

The incident occurred about 2:15 p.m. on the W&OD trail in the Ashburn area of Loudoun County, the county sheriff’s office said. The victim, described only as a man, was taken to the Lansdowne campus of Inova Loudoun Hospital and then to Inova Fairfax Hospital, the sheriff’s office said.

They said he was in stable condition.

According to the sheriff’s office, the victim was headed west and reportedly on the center line of the trail as he tried to pass two other cyclists. A cyclist going in the opposite direction purposely extended his arm and struck him on his helmet, the sheriff’s office said.

The westbound cyclist fell to the ground, the sheriff’s office said. The other cyclist rode off to the east, the sheriff’s office said, heading toward Ashburn Village Boulevard.

In a statement, the sheriff’s office said the suspect in what they described as an assault wore a white/light green shirt, a helmet and sunglasses, and was about six feet tall.

According to the office, his bicycle was said to resemble a time trial bike or a triathlon bike. The bars on the bike were “aero bars” and his helmet was an “aero” helmet covered with a sun shade that covered half his face, according to the statement.