The radar gun never lies. It is baseball's ultimate arbitrator, impartial by nature and honest to the point of brutality. It has rendered every Jered Weaver start this season a festival of incredulity, as if there's no way he really could be throwing this slowly.

Only here we are, in May, four full weeks of the baseball season past, and Weaver – 20-game winner and Cy Young runner-up within the past half-decade – is averaging around 83 miles per hour with his fastball. Considering the biggest in-season leap from April to the end of the year last year was 1.2 mph, the prospect of the 32-year-old Weaver regaining his velocity grows unlikelier by the day.

In certain parts of Texas, Weaver's fastball could travel along the interstate at its regular speed and not even draw an eye-blink from a state trooper, let alone a ticket. Of the 101 regular starting pitchers this season who throw changeups, 63 have intentionally slow pitches that move faster on average than a Weaver fastball. Since baseball installed pitch-tracking systems in its stadiums a decade ago, no right-handed non-knuckleball pitcher has thrown a fastball slower than Weaver this season.

The starkest change in baseball over the last decade hasn't been the proliferation of defensive shifts or the implementation of instant replay. In seven years, the mean fastball has gained 1 mph, up to 91.9. Relief pitchers average 93 with their fastballs. This is the Velo Era, where you throw hard and throw for strikes. Which leaves …

1. Jered Weaver trying on a Members Only jacket and popping the collar on his California Angels polo, because he's stuck in 83. It's not like this is all that new a phenomenon, either. As recently as 2011, Weaver's fastball sat around 90 mph. He never would win with pure velocity, but with his complement of pitches and funky delivery in which he steps across his body, Weaver could win so long as he commanded the ball well.

And he did, which is why when he started dipping to 88 the next season there wasn't immediate panic. It spent the next two years from 86-87 before cratering around 3 mph this spring and putting Weaver in some interesting company.

The only non-knuckleball pitcher to throw a slower fastball than Weaver since the PITCHf/x system started tracking velocity was Jamie Moyer. He was left-handed and closer to Social Security than his draft date. Baseball Info Solutions has Weaver's average fastball this season at 83.1 mph. Brooks Baseball, using a slightly different interpretation of the data, says 84.2 mph. Either way, it's bad, and perhaps nothing quantifies it as well as Brooks' data: The hardest fastball Weaver has thrown this year registered 87.81 mph. Of the 122 other pitchers who throw four-seam fastballs, 120 have a higher average velocity than Weaver's peak.

At least Weaver's descent to his current spot has gone in a linear fashion, without any of the frustrating gain-lost, gain-lost drama …

2. Justin Masterson has endured since arriving in 2008. For a 6-foot-6 monster, Masterson's fastball left his hand at a tepid 89.5 mph. He added three mph the next year and bounced up and down a mile or so a year. After spending April 2012 at 89.8 mph, he jumped to 92.1 in April 2013, only to fall back to 88.9 in the first month last season. His 1.7-mph dip this year, down to 87.2 mph, is the sixth-largest among starters who pitched last April, according to Baseball Info Solutions' data.

Story continues

After Masterson turned down a three-year, $51 million contract with Cleveland, he put up the worst season of his career last year, failing to replace his lost velocity with any semblance of control. Boston signed him to a one-year, $9.5 million make-good deal this offseason, and while he has managed to keep the ball in the stadium, the poor velocity isn't playing.

Masterson still can run it up – he maxed out at 91.7 mph on Friday, according to Brooks – but an average fastball of 87.5, on Brooks' algorithm that registers speeds higher than Baseball Info Solutions' no less, does not portend well, especially for a pitcher whose command waxes and wanes like Masterson's. It's the same issue …

3. Tim Lincecum faces as he copes with the single biggest velocity dip among starters this season: 2.5 mph. His drop ties that of Homer Bailey, who needs Tommy John surgery, but is actually bigger percentage-wise because he had less velocity to lose.

Lincecum's fastball today averages 87.3 mph. It's 0.1 mph faster than Masterson's, behind that of Jason Marquis, 103rd out of 112 qualifying pitchers. It's a dozen miles per hour off his peak, when Lincecum was unhittable at the University of Washington before he won a pair of Cy Young Awards with the San Francisco Giants.

His reinvention – the reinvention of any player whose velocity disappears – depends on his ability to command his pitches, and that still hasn't materialized. Lincecum at least has shown a willingness to adjust his pitch selection and work backward, throwing his changeup 30.8 percent of the time – fourth most among starters – and nearly doubling his curveball usage. If his fastball is no good, he may as well ditch it. That's tougher when you're like …

4. Mark Melancon and pretty much have only one pitch to throw. Melancon last year relied on a cutter about half the time, splitting the rest of his pitches between a four-seam fastball and curveball. He's ditched the fastball after it went from 92.8 mph last year to 88, albeit in a tiny sample. The cutter has a far bigger sample and is nearly as bad: 88.5 mph after sitting around 92 last year.

It could be Melancon, 30, is learning to pitch with lesser stuff. He has turned in four straight scoreless innings after imploding against the Cubs. The Pirates certainly could use Tony Watson in the closer's role, and Arquimedes Caminero is the second-hardest-throwing pitcher in baseball this season behind Aroldis Chapman.

Caminero's 98.6-mph has a full 10 miles per hour on Melancon's cutter, and that 10 miles buys a margin of error Melancon would love. Instead, he'll hope late movement does the same for him as it does for …

View photos Koji Uehara's fastball now averages 86.8 mph. (Getty Images) More

5. Koji Uehara with his split-fingered fastball. Uehara is the oldest player here, 40, and his fastball has ridden a parabola since he arrived in the major leagues in 2009. It sat at 86.9 mph that year, jumped to 88.1 the next, spent three years around 89, dipped back to 88.2 last season and averages 86.8 mph now.

As much of an issue as the velocity could be, what makes it so fascinating is that he's using his fastball as a changeup and his changeup as a fastball. Uehara has thrown his 78.5-mph split-finger fastball more than 75 percent of his pitches this season. And while that's likely to change, as Uehara hasn't even crossed the 10-inning threshold this season, it's a novel solution for the wear that time takes on the pitching arm.

It provides a great contrast, too, to …

6. Danny Salazar, who's more or less the Bugatti Veyron of starting pitchers, his speed barely street legal. Salazar, remember, was the rookie whom Cleveland started in the 2013 wild-card game and came out firing 100-mph darts. Something happened the next spring: Salazar wasn't throwing nearly as hard.

He was perfectly acceptable over the 20 starts he did make in 2014 with the Indians – a 4.25 ERA softened by 120 strikeouts in 110 innings – but this wasn't Salazar, world beater. His velocity last April was 93.6, and it ticked up only a mile at the end of the season. Now Salazar is sitting at 95-97 and hitting 100 again. His 2.4-mph gain on average velocity from last April is the biggest in the major leagues.

No surprise that Salazar leads all starters in baseball with 13.26 strikeouts per nine innings. The only other pitcher above the unlucky number: Indians teammate Carlos Carrasco, a fellow 2015 gainer with an additional 1.5 mph on his fastball from last April, at 13.21 per nine. They're the sort of numbers …

7. Mike Pelfrey never will approach, but at least he's looking more like his pre-injury self. Pelfrey, who arrived in New York with the hype of the next great Mets pitcher because of his big fastball, spent parts of five inconsistent seasons trying to show he was more than what the radar gun said.

Last season tested that: After hurrying back too quickly from Tommy John surgery, Pelfrey ended up with an irritated ulnar nerve that warranted surgery. The nerve pain had shot down his arm and dragged his fastball with it, all the way to 90.8 mph.

At the end of spring training this year, the Twins announced they would shift Pelfrey to their bullpen. He suggested they trade him instead. The Twins held tight, and the return of his 93-mph fastball validated them. Minnesota ended up putting Pelfrey in its rotation April 11, and he's got a sub-1.00 ERA over his past three starts, including seven shutout innings against a Kansas City offense hotter in April than anyone. The Royals have benefitted from velo jumps in the unlikeliest spot, too, with …

View photos Chris Young threw a hitless five innings against the Tigers in a spot start. (Getty Images) More

8. Chris Young of all people. That is the 6-foot-10-but-doesn't-throw-90 Chris Young, whose velocity ended up in the mid-80s and resigned him to the minor leagues until he figured out the problem himself.

As Andy McCullough detailed in The Kansas City Star, Young self-diagnosed thoracic outlet syndrome as the cause of his severe shoulder pain. A doctor took out a rib, relieving pressure that sent pain to the shoulder, and Young remembered what it felt like to throw harder. Not hard, mind you. His hitless, five-inning spot start for the suspended Edinson Volquez on Friday featured a fastball that Brooks said averaged 87.6 mph and topped out at 89.1. It's the kind of velocity …

9. Doug Fister has brought to the mound this season, a 2.1-mph dip that alongside Washington teammate Jordan Zimmermann's 1.5-mph drop isn't exactly the best news for the Nationals and is far worse for the free-agent prospects of Fister and Zimmermann.

Fister, 31, is set to be a free agent for the first time this offseason, and nothing has gone well. Over four starts, he hasn't generated the sort of ground balls he'd like and walked nearly twice as many as his career average. You want to have a 401k, not 4.01 Ks per nine like Fister.

Zimmermann, 29 this month, has even greater stakes. He came into this season likely to be the first pitcher with Tommy John surgery on his résumé to fetch a $100 million contract. Now, just about everything has gone wrong. Balls in play are dropping. Runners aren't getting stranded. Zimmermann's strikeout rate plummeted to less than six a game. His ERA of 4.88 doesn't scream nine figures. It could be the velo, or it could be the velo and something else, as seems to be the case with …

10. Jered Weaver and his straight fastball. According to Brooks' data, Weaver's fastball doesn't even move half an inch horizontally; straight fastballs can have the effect of looking like they're rising. So it can behoove pitchers with straight fastballs to throw them up in the zone and get hitters to chase what looks like a good pitch.

At 83 mph, Weaver is testing its effectiveness above the strike zone, and the early results aren't great. Of the 20 pitches hitters have swung at over the plate but above the strike zone, they've missed on just one. Weaver's whiff percentage in that area last season was 8.6 percent and 16 percent during his previous years.

Reinvention is the only way to save Weaver, unless like Pelfrey and Young it's an injury keeping him from mustering up anything more in his well-used shoulder. At some juncture, Weaver's survival instinct will kick in – perhaps soon, with one-strikeout games bookending his other starts this season. When it does, he'll have to answer a difficult question: Is he ready to put in the work necessary to move from crafty kid to out-and-out junkballer, who simply outthinks the hitters for a living?

It's there in him: the pitching savvy, the deception, all the stuff that made him so great when all he had in his arm was 90. Velo is king. It's why scouts raved about Adam Ottavino when he was up three mph from last year … only to suffer an elbow injury. Or why Jordan Walden's 2.5-mph drop from last April put the Cardinals on edge about what to expect from him before he was placed on the disabled list on Sunday.

So it goes in the Velo Era. If you don't throw hard, you get questioned, and even if you do throw hard, any falloff creates speculation. Jered Weaver went off a cliff this spring. The climb back to the top doesn't look promising.

More MLB coverage: