Defensive over-shifting has been a part of baseball ever since Lou Boudreau's Cleveland Indians started doing it in 1946 against Ted Williams of the Red Sox. Over the intervening decades, the occasional lefthanded hitting slugger has been treated to the Ted Williams shift but few teams have committed themselves so thoroughly as the Joe Maddon Rays and the Ron Roenicke Brewers the last couple of years. The Rays, by the way, were the No. 1 defensive team in baseball last year so it's hard to argue against Maddon's strategies. There is no true quantifiable way to measure the effectiveness of these shifting tendencies but stats maven John Dewan who compiles The Fielding Bible says batting average on balls hit into the shift has declined by 40 points.
Lawrie makes Jays shiftier
Toronto Sun | Apr 24