4. Trevor Williams - Washington Nationals
The Washington Nationals have not experienced a ton of winning this year, and it is unlikely that will change any time soon. However, the trade deadline is one area where the Nats could be clear winners. As Washington continues to fall further back from contention, they should begin to receive inquiries about the availability of Trevor Williams if they have not already.
Williams is in the midst of the best season of his nine-year career, sporting a 2.29 ERA, 1.078 WHIP, and 7.6 strikeouts per nine innings. This is easily his best performance, exclusively being a member of a team's starting rotation and one that should warrant contending teams attempting to trade for him as they look to make their playoff push.
The only real concern here is the longevity of Williams' early-season performance. Williams is 32 years old and pitching far better than he has at any point in his career. Considering that he gave up a National League-high 34 home runs last season, there are some real concerns about possible regression as the season continues. But if he is able to prevent the long ball and keep pitching at this level, Williams could be a difference-maker for a contender come playoff time.