The fact that there isn't a measurement actually adds to the mystique. It was in a spring training game when Tyler O'Neill hit a Clayton Kershaw fastball over the fence, over the bullpen, over the umbrellas on the picnic tables and into the ether of estimation. I'm thinking the Canadian hit it at least a kilometer.
O'Neill is a current Cardinals outfielder and could face Kershaw tonight, when the lefty returns to Busch Stadium to face St. Louis. But O'Neill's homer in the spring of 2017 was an emphatic way for O'Neill to introduce himself to the casual baseball fan, hitting a homer that made Twitter atwitter.