I was watching a Twins broadcast and the announcers were discussing Aaron Hicks's struggles at the plate. Through May 11, Hicks was batting .160 with a .235 slugging percentage. That's pretty bad; among pitchers with at least 15 plate appearances, 13 are batting and slugging higher. (Hicks has heated up since, going 7-for-21, but his batting average is still below .200.) The announcers were reminiscing about Twins great Harmon Killebrew. One of them, I think it was Bert Blyleven, said that when Killebrew would visit the batting cage after he retired, his advice to hitters was, "Keep swinging." The announcers talked about how Killebrew was a free swinger but when he made contact the ball went a long way.
Today, we have the technology to precisely measure that. Tigers rookie Nick Castellanos leads the majors in swinging, having swung at 59.3% of the pitches thrown to him. The Cardinals' Matt Carpenter is the other extreme, swinging 33.6% of the time. So Castallanos keeps swinging, while Carpenter doesn't. But pitch-by-pitch data weren't available in the 1950s, 60s, and 70s when Killebrew played. So we'll have to go by strikeouts and walks.
Obviously, a guy who strikes out a lot is taking a lot of swings. Killebrew struck out 1,699 times in his career, 27th most all time. He led the AL in strikeouts once and was in the top ten seven other times. But does that make him a free swinger?
Not if you look at his bases on balls. Killebrew is 15th all time with 1,559 walks. He led the American League in walks four times, was in the top three eight times, and in the top ten 13 times. In his years as a regular (1959-1972), among players with at least 1000 games played, Killebrew had the 24th lowest ratio of strikeouts to walks in the majors. Compared to his walks, he struck out less frequently (1.01 strikeouts per walk) than Pete Rose (1.03)!
So whoever heard him say, "Swing away," must've missed when he added "at pitches you can hit; otherwise, take your base on balls."