Each week, FantasyPros publishes a fantasy baseball trade chart. The chart contains player values designed to help you assess the overall weight of both sides of a trade.

The weekly trade charts also keep track of the changes in a player’s value from the previous week. But sometimes, the reasons for a change aren’t obvious. “Why is player X gaining three points in value this week when player Y, who had an even better week, remained the same?”

Good question, reader. There are many answers as to why any given player moves in value from one week to the next. And in this article, we’ll examine some of the biggest risers and fallers each week, and explain the movement.

Here are some of the most notable risers and fallers in the FantasyPros Week 9 Trade Value Chart:

Risers

Julio Rodriguez (OF – SEA). Week 9 Value: 23. Previous Value: 18. Change: +5

One of my faults as a fantasy manager and analyst is that I am reluctant to buy into young players until they essentially leave me no choice. And that’s what we’ve got here with Rodriguez.

Other than keeper and dynasty formats, I didn’t have a ton of interest in Rodriguez during draft season. A 21-year-old with 46 games in Double-A? We loved the speed but the odds of a player like that having a successful rookie season are low.

And that’s what we saw in April. A .205/.284/.260 slash line with a 37% strikeout rate and no home runs. Yes, there were several unfortunate called third strikes and he had nine steals, but still, chances of success looked slim.

No longer. He followed up his slow April by slashing .309/.339/.527 in May and now .348/.444/.522 in June. He’s up to seven home runs and he continues to run with reckless abandon, and is now up to 17 steals.

He still strikes out too much and his xBA (.253) is nearly 25 points lower than his batting average. But his max exit velocity – essentially his raw power – ranks in the top five percent of MLB. And more importantly, he ranks in the 98th percentile in sprint speed. And while many youngsters get gunshy on the basepaths even with elite speed, Rodriguez obviously doesn’t have that problem.

He’s been slowly rising all season and will continue to do so.

Framber Valdez (SP – HOU). Week 9 Value: 18. Previous Value: 12. Change: +6

The thing about Valdez is you can’t watch him pitch. Because if you do, you’re going to see random bouts of wildness where he just doesn’t seem to know where his pitches are going, and you’re going to turn the TV off in frustration and wonder why you’re rostering him.

There are problems for Valdez, for sure. He generally still walks too many hitters and his strikeout rate is a career worst 19.6%. Meanwhile, although he’s outstanding at limiting home runs, his 0.39 HR/9 rate has to regress a bit at some point.

But, I mean, the guy has a 65.5% ground ball rate. And although that’s down from last year’s 70.3%, it’s still the best in the majors by far. And part of the reason Valdez’s strikeout rate has dipped so much is because it’s a lot more efficient to just get ground-ball outs all day, which is why he is averaging roughly 6 1/3 innings per start.

Indeed, Valdez has gone at least six innings in nine straight starts, and he hasn’t allowed more than three earned runs in any of them. And the benefit of going deep into games is twofold: he has the opportunity to earn more wins, as he has done in each of his past five starts, and the impact of his stellar numbers is magnified even more.

Valdez has little chance of ever cracking the top 10 fantasy starters. But he is incredibly reliable right now, enough to make him worth targeting in a trade.

Luis Severino (SP – NYY). Week 9 Value: 14. Previous Value: 9. Change: +5

I’ve been unfair to Severino in the trade chart thus far, and I may still be. I mean, the guy has effectively missed three full seasons, so in addition to worrying about his injury risk, it’s just difficult to imagine that he can be the incredibly effective pitcher he once was.

But, yeah, this does look a lot like the old Severino. A 2.95 ERA, a 1.00 WHIP, strong strikeout and walk rates. And there’s now a reason for us to buy into his performance as real.

Back in his heyday, Severino threw his slider about 35% of the time, give or take. It was an elite pitch, one that batters had difficulty squaring up or even making contact with. But for a pitcher coming off multiple arm injuries, it seemed unlikely that he would lean into a pitch that is notorious for putting stress on an elbow.

And, indeed, Severino has thrown his slider just 16.7% of the time this year. But recently, he has upped the usage of that pitch significantly. Over his last five starts, he has thrown his slider 20.6%, 12.6%, 28.7%, 20.4%, and 26.4%. That’s a far cry from his peak usage, but also much more than we had seen at the beginning of the season.

Severino throwing his slider more likely means more success, but it also means that he is feeling confident in the health of his elbow. And both of those things means an increase in trade value.

Fallers

Walker Buehler (SP – LAD). Week 9 Value: 29. Previous Value: 34. Change: -5

Players like Buehler with a lengthy history of success will often get a pass for any early season struggles. Absent an injury, it’s prudent for fantasy managers to dismiss a slight downturn in performance to a small sample size, or at least for them to trust that the player will diagnose the issue.

But things have gone on long enough with Buehler that it’s time to start downgrading him a bit. The base numbers (3.84 ERA, 1.31 WHIP) are the worst of his career, as too is his 20.2% strikeout rate.

To put his drop in strikeouts into perspective, Buehler has a career 26.9% K rate, and his lowest single-season mark is 26%. And his whiff rate is down on all of his pitches other than his slider.

We could dismiss this as a small sample size, but the truth is, there’s a pretty fair reason for his drop in strikeouts. All of his pitches have seen a precipitous drop in both velocity and spin rate.

For example, Buehler’s spin rate on his fastball is 2266 RPMs. Prior to this year, the lowest mark of his career was 2415 RPMs. His curveball and cutter are down 200 RPMs from last year alone.

Maybe it’s the ban on sticky stuff, maybe it’s just an early season lull. But whatever it is, Buehler is not the same pitcher that we thought he would be heading into the season.

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Dan Harris is a featured writer for FantasyPros. For more from Dan, check out his archive or follow him on Twitter @danharris80.