Washington Nationals Catcher Keibert Ruiz Struck In Head By A Foul Ball

A frightening moment went down in the Nationals' dugout on Monday ... when catcher Keibert Ruiz took a foul ball off the side of the head -- forcing him to exit the game and head to the hospital for a CT scan.

It all unfolded during the Nats' tilt against the San Diego Padres in the top of the fourth inning. Washington designated hitter Josh Bell fouled off a 91 MPH cutter, sending it directly into the Nationals' bench.

Everything seemed fine ... with one of Washington's coaches even cracking a smile toward Bell -- but Ruiz was then shown on the game's broadcast heading down the tunnel, grabbing the right side of his head.

After defeating the Padres 10-6, Nationals manager Dave Martinez met with the media ... and revealed Ruiz left the ballpark for further evaluation at a local hospital.

"The ball hit him pretty solid on the side of the head," Martinez said. "We all ducked and when he went down, we kind of got scared a little bit. He had a nice lump on the side of his head. A little concerned right now. Hopefully, he comes out of it OK."

While we await an update on the 26-year-old's condition ... it marks the second time in nearly a week a player was injured by a foul ball while sitting in the dugout.

Tampa Bay Rays pitcher Hunter Bigge was struck in the face by a 105 MPH line drive foul ball ... knocking him off his feet. He was carted away and taken to a medical facility.

Bigge ended up being released from the hospital on Saturday.