A story was told in the June 12, 1947 New York (NY) Times about Yankees baseball player Yogi Berra (1925-2015) that manager Bucky Harris (who first managed the Yankees in 1947) told Berra to think and not to go after bad pitches. “How can a guy hit and think at the same time?” Berra complained.
 
Berra wrote in The Yogi Book: I Really Didn’t Say Everything I Said! (1998) that he first said the line in 1946 to his manager on the Triple A Newark Bears.
 
“A full mind is an empty bat” and “When you think, you stink” are related sayings.
 
[This entry includes prior research by the Quote Investigator.]
   
 
Wikipedia: Yogi Berra
Lawrence Peter “Yogi” Berra (May 12, 1925 – September 22, 2015) was an American professional baseball catcher, manager, and coach who played 19 seasons in Major League Baseball (MLB) (1946–63, 1965) (all but the last for the New York Yankees). He was an 18-time All-Star and 10-time World Series champion as a player. Berra had a career batting average of .285, while compiling 358 home runs and 1,430 runs batted in. He is one of only five players to win the American League Most Valuable Player Award three times. He is widely regarded as one of the greatest catchers in baseball history, and was elected to the Baseball Hall of Fame in 1972.
 
12 June 1947, New York (NY) Times, “Sports of the Times: Short Shots in Sundry Directions” by Arthur Daley, pg. 34, col. 7:
One Job a a Time
Yogi Berra of the Yankees is also a character and a mighty colorful one, too. Not very long ago Bucky Harris was searching for a pinch-hitter and his eyes roamed up ad down the bench before stopping. They rested on the squat and muscular Berra.
 
“You, Yogi,” snapped Bucky. “Go in there and hit. I realize that you’re in a slump, but you aren’t thinking enough at the plate. Think before you pick our a ball. Make sure it’s good before you swing. Think!”
 
The Yankee manager gave his hero a brisk pat on the back and sent him into the fray. Yogi struck out most inelegantly and stamped angrily back to the bench, muttering away to himself in a corner of the dug-out. After a while the curious Bucky wandered down and listened to him.
 
Yogi was repeating over and over, “How can a guy hit and think at the same time?”
 
Google Books
September 1950, Boys’ Life, “Scouting the Sports Scene” with Stanley Pashko, pg. 39, col. 3:
It seems that the Yankee brain trust was disturbed about Yogi’s inability to let any kind of pitch go by unmolested. They called him away from the plate in one game, telling him not to go for bad pitches. “When you get up there,” they admonished, “think—think—think.”
 
Yogi went up, took three called strikes, and returned to the bench.
 
“How can anybody think and hit the ball at the same time?” he complained.
 
Google Books
The Yogi Book:
I Really Didn’t Say Everything I Said!
By Yogi Berra
New York, Y: Workman Publishing
1998
Pg. 13:
“You can’t think and hit at the same time.”
If you ask me, this is true with any sport. I said it in 1946 when I was with the Newark Bears playing Triple A. My manager told me not to swing at balls out of the strike zone. He said, “Yogi, next time you’re up, think about what you’re doing.” I struck out in three pitches!

Google Books
The Yale Book of Quotations
Edited by Fred R. Shapiro
New Haven: Yale University Press
2006
Pg. 58:
Yogi Berra
U.S. baseball player and sage, 1925-
(...)
How can a guy think and hit at the same time?
Quoted in Wash. Post, 27 Jan. 1952. Berra writes in

(1998) that he said this in 1946.
 
USA Today—For The Win
The 50 greatest Yogi Berra quotes
By: Nate Scott | September 23, 2015 7:30 am
(...)
16. How can you think and hit at the same time?
 
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How can you think and hit at the same time ~ Yogi Berra
9:26 AM - 20 Sep 2016