As most of you already know, Madison Bumgarner made his big league debut Tuesday night, pitching into the sixth inning with no decision in the Giants’ 4-3 loss to the Padres. That’s big news, for several reasons.

First, let’s appreciate that Bumgarner has been the best pitcher in the minor leagues the last two seasons—and it’s really not close. The lefthander is 27-5, 1.65 over 273 innings in 2008-2009, with 107 innings coming this year at Double-A Connecticut. Bumgarner has a sterling 256-to-55 strikeout-to-walk ratio overall and gave up just nine home runs in the minors, though he allowed a pair in his debut last night.

While Bumgarner maintained a sterling strikeout rate in the high Class A California League earlier this season, his rate dipped to just 5.8 per nine innings in the Eastern League. The main culprit for that decrease has been the decreased fastball velocity that was on display last night in the big leagues. He threw 76 pitches, according to MLB’s Pitch F/X data, and 48 were fastballs, most of which checked in around 88 mph.

That’s consistent with what Eastern League managers and scouts are saying about Bumgarner. One scout, who also saw Bumgarner as an amateur at South Caldwell High in Hudson, N.C., said Bumgarner didn’t quite have the arm and hand speed now that he saw back in 2007, when the Giants took the lefthander the 10th overall selection. He also didn’t think the decrease in velocity was anything to worry about, not yet anyway.

"He threw a lot of 87s and 88s when I saw him and touched some 90s, but he still really pitched off the fastball," the scout said. "It was almost more encouraging to see him pitch that well using pitchability rather than just getting by on pure, raw stuff.

"I wouldn’t say he’s got a dead arm period, but I think it’s just the natural period that all young pitchers go through in their first or second year, when they lose a little arm speed (and) have to pitch through some fatigue."

This scout attributed Bumgarner’s success to his ability to create difficult angles for the hitter, command the fastball and maintain the pitch’s excellent late life. He said he’d still grade out Bumgarner’s fastball as above-average, even with velocity that was just average.

"He uses the fastball so well, and he’s got some deception," the scout said. "He throws a little across his body but not terribly, and he’s got that life and command. The thing is, so many young pitchers get exposed at upper levels because they don’t know how to pitch off the fastball. And when hitters don’t chase their secondary stuff when it’s out of the zone, they often don’t know how to pitch off the fastball. Or you’ll see that their fastball is really true and doesn’t have good enough life, or they don’t command it.

"He does those things already. He knows how to pitch off the fastball. We’ve seen him pitch at 93-94 miles per hour when he’s at his best, and I’ve seen him have a plus breaking ball when he stays on top of it, though it was inconsistent when he was an amateur. I didn’t see a great breaking ball when I saw him this year. But he still pitched very well because of the quality of that fastball, and I think we’ll see that electricity come back."

Bumgarner may turn out to be a major test of just how successful a starting pitcher can be working off one plus pitch, provided that pitch is the fastball. He’ll have to maintain the premium life and command the pitch exhibits while getting back to his old velocity to be a front-line starter. No matter how he develops, he’s unlikely to match the dominant numbers he posted as a minor leaguer.