Jim Henderson only threw 5 pitches in his outing on Tuesday (4 being fastballs), but a very quick look at his fastball velocity average, low, and high on his Fangraphs Pitch f/x chart does not look very promising. His average on those four fastballs was lower than only a handful of his career appearances, and his hardest thrown of the 4, around 95 mph, was lower than all but 1 other regular-season appearance: oddly enough, his major league debut.
So do we have a problem? I am not so sure. Henderson may be a guy that just takes a bit longer in the spring to get to his peak velocity. It's possible that Roenicke just happened to notice it this year. To show you what I mean, I whipped up a chart with 4 items: Fastball velocity in order from Tuesday's appearance, his outing at Miller Park against the Royals last weekend that was recorded by Pitch F/x, and data from a similar exhibition pre-season last year against the White Sox, and his overall average fastball velocity from last year. He didn't top his usual average with any one pitch in any of the three games.
It's not totally isolated, either. A World Baseball Classic game that was tracked by Pitch f/x earlier last spring showed him with even lower velocity, which would be expected in early March.
Last year, Henderson jumped back towards his season velocity average in his second appearance and stayed there until he came into a bit of a summer lull for a few games, then bounced back later in the season.
The takeaway here is that we have one other year of early-season data for Henderson, and that he also got off to a slower start last year and ended up okay. We will be keeping an eye on him over the next few outings, but I suspect that we may see him round back into form. If the velocity stays down into the middle of April, that's when we might now we have a problem.