Who knew a few ounces could make such a difference?

Marcus Semien has been having his best season as a pro, on pace to set career-highs in batting average (.273), on-base percentage (.359), and wins above replacement (5.7).

What has been the key to Semien’s breakout season? He made a switch in the weight of the bat he uses at the plate. He recently explained the changes to Marcus Thompson of The Athletic: 

Part of Semien’s improvement at the plate is credited to a bat switch. Last season, Semien used a 34-inch bat. But this spring, he switched to 33.5 inches. He said the smaller bat made his hands feel quicker.

Then, on June 7 in Arlington, Texas, he got a lighter version of the new bat, dropping down to 31.5 ounces. That night, Semien went 4 for 5 with two home runs and drove in four of the A’s runs in a 5-4 win over Texas.

Since that day in early-June, Semien is hitting .287 with 15 home runs and 33 runs batted in. 

“The first game I used it,” Semien told Thompson. “I was like, ‘I’m sticking with this bat.'”

The former Cal baseball standout also has focused on his launch angle and exit velocity, allowing him to improve his power numbers.

“If you’re pulling it down the line,” he explained, “all you’ve got to do is hit it 95 (miles per hour) with a 27 (degree launch angle) and it’s a home run. Because I don’t hit the ball like (Aaron) Judge or them dudes that hit it 115 (mph)."


“I can’t hit it that hard. But if you hit it at the right angle, a home run is a home run.”

Semien’s defense also has dramatically improved. After playing the majority of his career at third base with the White Sox, Semien took over as primarily a shortstop in 2015 after being included in the Jeff Samardzija trade. 

Semien proceeded to lead the league in errors with 35 in 2015, posting a fielding percentage of just .947. He’s made major strides since then -- posting a career-high of .980 so far in 2019 -- placing him above the league-average of .970 for shortstops.

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“This is a self-made guy,” A’s manager Bob Melvin said. “Once he took off with (former third base coach) Ron Washington and found the work ethic and fundamentals of the position, it’s been him. He’s had quite a few guys working with him. But his understanding of what he needs to do and how he can better is unlike anybody I’ve ever been around.”

The A’s are hoping those fundamentals can help them secure a playoff spot in the AL, where they currently sit in a tie for the second wild-card spot.