Dan Jennings was probably hoping Pittsburgh Pirates shortstop Jordy Mercer would offer at the 93-mile-per-hour fastball and swing and miss for strike one.

Maybe send a ground ball to an infielder for the second out of the seventh inning of a game his Miami Marlins trailed 5-0. Or perhaps lift a fly ball to right field.

But a screaming line drive headed to the left side of Jennings’s head? No one expects that, even though we’ve seen it happen far too often the past few years in the major leagues.

The left-handed relief pitcher was struck by a ball reportedly travelling 101 mph. The ball deflected off Jennings’s head and straight up in the air, eventually caught by shortstop and former Toronto Blue Jay Adeiny Hechavarria behind second base.

Upon falling to the ground, a disoriented Jennings ripped off his ball cap, rose to his feet and hunched over at the front of the mound. Marlins catcher Jarrod Saltalamacchia arrived and helped Jennings to one knee while keeping him balanced.

Jennings was taken off the field on a cart and raised his right hand to the stunned and silent crowd at PNC Park in Pittsburgh to indicate he was fine.

“He was responding to the questions [Marlins trainer] Sean [Cunningham] was asking him,” said Miami manager Mike Redmond of the 27-year-old Jennings, a ninth-round draft pick in 2009 who’s in his third season with the Marlins.

A CT scan was negative and Jennings, who spent the night in hospital for observation, was diagnosed with a concussion.

“I’ve never been on the field when something like that has happened. … It’s scary,” Saltalamacchia told reporters. “It goes past baseball and you start to worry about life. He’s got a wife and kid.”

Unlike Saltalamacchia, Redmond has been on the field for a similar incident. In 2003, he was the catcher for the Florida Marlins when teammate Kevin Olsen was struck on the side of the head by a Todd Walker line drive in Boston. Olsen never pitched in the majors again after that season.

The Jennings incident reminds us of recent injuries to pitchers J.A. Happ of the Blue Jays, Alex Cobb of the Tampa Bay Rays and Brandon McCarthy, then of the Oakland Athletics and now a member of the New York Yankees.