If your league doesn't have a trade deadline before September (or at all), you still have plenty of time to wheel and deal for the playoff stretch. Most of us, however, are up against Father Time and his ceaseless battle to rob us of our most precious commodity. If you're in the market to make a last-second deal that could swing the tide for you in one category or another, here are some names to consider adding or moving.

Scouting players who may be undervalued and re-assessing players who may be overvalued is a weekly exercise that you should constantly pursue as a dedicated fantasy baseball manager. Fortunately, I have you covered. Here are a few players who are good buy or sell candidates based on their current performance compared to ownership levels. This could mean scooping them off waivers if possible or actively seeking a trade to acquire or discard certain players in order to maximize value.

I will never advocate that you buy or sell a player if I wouldn't follow the same advice myself. Now, time to assess some fantasy values.

Undervalued Players - Week 20

Derek Dietrich (1B/2B/OF, MIA) 48% owned

Last Man Standing. That may be Dietrich's new title soon, as he is one of the few Marlins from last season to remain on the roster and continue to see regular playing time. While he's not a valued young prospect like Brian Anderson or an established veteran like Martin Prado, Dietrich has the distinction of batting cleanup behind J.T. Realmuto now. Sure, the Marlins are the second-lowest scoring team in the majors, but they do score on occasion and Dietrich has enough pop with his 14 homers to be an adequate streamer at any spot. A move to first base in place of Justin Bour just adds to his positional eligibility and makes him more appealing in leagues that play 12 or more offensive players.

Aledmys Diaz (SS, TOR) 20% owned

It's easy to forget that Diaz was an All-Star just two seasons ago. He has since struggled with injuries and fastballs, but there have been positive signs in Toronto both early and late this year. Diaz had a brief power surge in April and looked ready to recapture his old form before slumping to a .183 average that month. He then missed three weeks on the DL and found himself battling for playing time with fellow Cuban Lourdes Gurriel. Now that Gurriel is injured, Diaz has taken the job and run with it, batting .313 with six homers, 13 RBI and a pair of steals over the past month. He is an aggressive hitter (77% Z-Swing%) on a free-swinging team who hits too many ground balls to be a true slugger, so he will continue to be prone to peaks and valleys. Take advantage while he's hot if you need a boost in the middle infield, but don't necessarily count on him in September.

Mallex Smith (OF, TB) 52% owned

It goes without saying that if you need a speed boost, there are precious few commodities available to pursue these days. Only 14 players have reached the 20-steal threshold and Trea Turner is the only one to hit 30 so far. I posited back in April that Smith had 40-steal potential and Kevin Kiermaier's continued injury troubles only reinforced that notion once Smith became an everyday outfielder. Fast forward and Smith is at 25 SB on the year, but that has come with a .300 average (eat your heart out B-Ham) that has given fantasy owners an unexpected boost. After a mid-season lull, Smith is turning on the jets lately with seven steals in the past week. The Rays finally made the wise decision to put him in the leadoff spot and it has made all the difference for him. With greater run-scoring potential, Smith should prove to be a more valuable version of Dee Gordon down the stretch and should be added over struggling players like Billy Hamilton or Ender Inciarte.

Fernando Rodney (RP, OAK) 68% owned

Undervalued his whole career? Arguably, but let's look at 2018 in a vacuum. Rodney was overlooked all preseason, selected as the 83rd pitcher and 220th overall player off the board in NFBC leagues, behind deposed closers Brad Brach, Greg Holland, and Mark Melancon. All he's done is save 25 games and keep his ERA around 3.00 with a 10.3 K/9. A completely expected trade out of Minnesota might seem to kill his value since he's not the lone candidate for saves anymore, but don't give up on him just yet. Blake Treinen has been lights out this year, but all it takes is an injury or a couple of blown saves before the vet could find himself saving games in Oakland. If you have room to make him a bench stash, do it rather than cutting bait right away and consider him a high-end closer handcuff for a contending team.

Overvalued Players - Week 20

Carlos Santana (1B/OF, PHI) 81% owned

The Phillies got Justin Bour, eh? Interesting that they would add a power-hitting, left-handed first baseman who mashes righties while Santana is hitting just .209 vs RHP. Santana probably won't be entering a strict platoon, but he could face more days off through the second half. That aside, let's talk about his .217 average and the fact he barely ranks within the top 20 first baseman with 17 HR. His 127 R+RBI keep him as a valuable fantasy piece, but there's a clear tradeoff here. I've harped on this before in this column, so let's leave it at that for now. Santana outstanding walk rate and OBP do nothing to help most fantasy owners, so you have to evaluate your needs at this point. If you need a boost in average rather than RBI, trade Santana away in exchange for a player like Jesus Aguilar.

Matt Kemp (OF, LAD) 76% owned

Speaking of Father Time, it looks like Kemp got jumped by him on his way back to Dodger Stadium to start the second half of the season. Kemp is batting .180 since the break and now has an ankle contusion to deal with. The slew of deadline deals the team made to improve offensively render Kemp far less useful than he was earlier in the year when everyone was slumping and/or hurt. He is no more than a platoon bat at this point and should be sold off for whatever price he could possibly fetch.

Sonny Gray (SP, NYY) 42% owned

Mercy be to the 42% of you that have either kept the faith or stopped checking your fantasy baseball team months ago. Sonny Gray has made Jon Gray's (no relation) inflated ratios look somewhat decent by comparison. After another disastrous start on August 1, against the Orioles no less, Gray has been moved to the bullpen. This just means he has fewer innings to eat up in between those homerfests. Clear up some roster space and then just pretend you never drafted or picked him up in the first place.

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