He played in Major League Baseball (MLB) for the Texas Rangers, Chicago Cubs, Baltimore Orioles, Houston Astros, Toronto Blue Jays, and Cincinnati Reds.

[9] Feldman lost 40 pounds (18 kg) before the start of his freshman year at the College of San Mateo, and walked on to the team.

[15] He began the 2005 season with the Single-A Bakersfield Blaze, but after nine scoreless innings in relief was quickly promoted to the Double-A Frisco RoughRiders.

[18] With the RoughRiders, he held opposing batters to a .202 batting average in 46 relief appearances, led the team with 14 saves (which tied for fifth-most in the league), and had a 2.36 ERA.

[19] Prior to the 2006 season, MLB.com beat reporter T. R. Sullivan opined that Feldman was the Rangers' top minor league relief prospect.

I didn’t know what to expect, but when I walked in [the locker room], I saw a lot of the guys I had seen on TV all these years, and was like, 'Holy cow, I’m in the big leagues'", he remembers.

Suddenly, unable to continue the prank any longer, Showalter burst out laughing: "Pack your bags, rookie, you’re coming with us!

Tensions between the two division rivals were already high after two Ranger starting pitchers — Adam Eaton and Vicente Padilla — had been ejected in previous games that month for throwing at Angel hitters, along with Texas manager Buck Showalter.

"[28] Rangers play-by-play announcer Josh Lewin even commented on Feldman's side arm punch, stating "He's a sidearm puncher too."

Instead of throwing sidearm, he raised his arm angle and threw from a three-quarters delivery, which pitching coach Mark Connor observed gave him more sink on his fastball and downward movement on his breaking ball.

"[36] In late March, he was one of three pitchers vying for one long relief spot on the team, though the Rangers also began experimenting with converting him to be a starter.

[37] General Manager Jon Daniels observed: "Toward the end of spring training something clicked with his new [three-quarter] arm slot.

This was the first time a major league pitcher gave up at least 12 runs without taking a loss since Gene Packard of the St. Louis Cardinals did it on August 3, 1918).

"[44] General Manager Daniels noted: "Feldman has really saved our pen this year, and he wasn't a guy we were counting on in the beginning of the season.

[19][47] His 13 unearned runs tied for the third-highest total in the AL.[19] During the off-season, club president Nolan Ryan emphasized conditioning for the Rangers pitchers.

[52][53] In early May, Washington noted: "He has real life on his fastball, his slider is harder than it has been, his breaking ball is much crisper, and he's getting a good feel for his changeup.

[56] On July 25, Feldman outpitched Kansas City All-Star and AL ERA leader Zack Greinke with eight innings of four-hit, shutout ball, leading the Rangers to a 2–0 victory.

[59] After he beat the Mariners on short (three days') rest at the beginning of August for the team lead in wins, Seattle manager Don Wakamatsu said: "I thought Feldman was awfully tough.

"[62] And two days later, Phil Rogers wrote for The Chicago Tribune: "Scott Feldman is creeping into consideration for the bottom of Cy Young ballots.

[72][73] Evan Grant, writing for D Magazine, asked rhetorically: "At some point, RHP Scott Feldman is going to have to enter the Cy Young Award conversation, isn't he?

[75] He struck out five, while giving up five singles, raising his record to 16–4, and tying Sabathia and Verlander for the AL lead in victories.

"[82] And Jennifer Floyd Engel of The Fort Worth Star-Telegram wrote: "Is there a more likable "stud player" on any of the locals than Scott Feldman?

Dude is amazing, wins freakishly a lot on the road, is Boy Scout-ishly dependable, has been an ace on what is really a pretty good staff, and is humble as hell.

[87] As of mid-September, Feldman's cutter was still the third-most-effective pitch in the major leagues, behind only Tim Lincecum's changeup and Randy Wolf's fastball.

[90] He was named the Texas Rangers' Pitcher of the Year for 2009 by the Dallas-Fort Worth Chapter of the Baseball Writers' Association of America.

[96] However, on July 14, after he cleared waivers, Feldman rejected the assignment giving the Rangers the option of activating him from the disabled list or releasing him.

[99] Brought in during the first game of the playoffs against the Tampa Bay Rays, he pitched three scoreless innings, allowing two hits while striking out four.

[13] On July 2, 2013, Feldman and Steve Clevenger were traded to the Baltimore Orioles for pitchers Jake Arrieta and Pedro Strop.

[9] He received the Astros 2014 Darryl Kile Good Guy Award, voted by the Houston Chapter of the Baseball Writers' Association of America.

On August 1, 2016, Feldman was traded by the Astros to the Toronto Blue Jays for minor league pitcher Guadalupe Chavez.