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 13 Trade Value Chart:

Risers

Julio Rodriguez (OF – SEA). Week 13 Value: 29. Previous Value: 23. Change: +6

My guess is that despite this rise in value, most fantasy managers still believe Rodriguez should be higher. Yes, he’s now valued as a top-30 player, but I’ve seen many argue that he should be drafted as a first-rounder if we did it all over again now.

To be fair, there’s not a strong argument against it. He’s on pace to go 30-40 while batting .275. His 92.1 MPH average exit velocity and 50.2% hard hit rate are both in the top nine percent of baseball. He’s outstanding.

But he’s a baby, and there are just a few things that give me enough pause to keep him out of the truly elite. His ground ball rate of 48.4% may wind up keeping his home runs in check just a bit going forward, and his 6.9% walk rate leaves him with just a .335 OBP. You can be a prolific base-stealer getting on base that infrequently, but it’s tough to do.

Most importantly, there’s just not that much of a gap between the 30th-ranked player and the 15th-ranked player. Rodriguez is elite. Trade for him with confidence.

Bryan Reynolds (OF – PIT). Week 13 Value: 15. Previous Value: 10. Change: +5.

Let’s call this fun with slash lines. Here are Reynolds’ month by month numbers:

• April: .194/.293/.306
• May: .224/.309/.449
• June: .333/.379/.610.

Sometimes hitters are just cold. Simple as that. And although there isn’t always an equal hot streak to balance out a cold streak, more often than not, a player’s performance will regress to the mean.

That’s essentially what we’ve got with Reynolds. He isn’t as bad as he showed in April and May. He isn’t as good as he showed in June. But when you add it all up, it’s a pretty good player. Simple as that. And his value should therefore rise to roughly preseason levels.

Tony Gonsolin (SP – LAD). Week 13 Value: 10. Previous Value: 5. Change: +5.

It takes a lot for me to move a guy like Gonsolin up in trade value. He’s been a fine pitcher his whole career, but he has never pitched more than 55 2/3 innings in an MLB season or started more than 13 games in a season. The Dodgers often have an embarrassment of riches at pitcher and they make the most of them.

But Gonsolin has been pretty incredible this year. A 1.54 ERA, a 0.82 WHIP, 10 wins, and career-highs in innings pitched and starts. He deserves to be a valued trade chip.

But let’s hold the phone on annointing him an elite starter. He has a 2.81 xERA, a 3.30 FIP, and a 3.77 xFIP. Even if you could buy his performance, there’s just not much chance he can get past 130 – 140 innings this season given how light his workload has been for years.

If you need ratios and wins, you can certainly buy Gonsolin. Just keep the price in check.

Fallers

Tarik Skubal (SP – DET). Week 13 Value: 7. Previous Value: 12. Change: -5

Skubal has really hit a rough patch of late. He’s allowed at least four earned runs in four of his last five starts. At least five earned runs in three of his last four starts. His once-pristine ERA is all the way up to 4.06.

There is a lot to like about Skubal. He doesn’t offer many free passes and his walk rate continues to improve. He’s cut way down on the quality of contact allowed to opposing hitters. His strikeout rate is solid.

But if you’re pitching for the Tigers, you need to be borderline dominant to allow for fantasy managers to target you in a trade. And Skubal is far from that, especially lately.

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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.