Even as a fan of the team throwing to first, I sometimes get annoyed with the process. It breaks up the flow of the game, it seemingly never works, and yet teams continually do it. Is it actually effective as a tactic or is it another practice in baseball that's done because it's always been done?
As of late June (can't find more recent stats), both Andy Pettitte and A.J. Burnett were near the top of the league in pick-off attempts. Burnett had a game this year against the Angels in which he threw to first base 24 times in 7 innings. They do get results though, as Pettitte is tied for the AL lead with 8 pickoffs this year while Burnett is not too far behind with 5. However, Burnett has more pickoffs where the runner was tagged out diving back to first base (4) than Pettite (3), probably because runners are more wary of Andy's move. Five of Pettitte's PO's were of the variety that CC Sabathia recorded against Jacoby Ellsbury last Sunday Night in which the runner was going on motion and got caught stealing.
We all know that pickoffs are pretty rare. Pettitte has allowed 178 runners to reach first base this year via single, walk or HBP and has nabbed less than 5% of them, or fewer than one every 3 starts. Much of the time the throws to the base are called from the bench and it's not especially close. You essentially never see a runner picked off the second time the pitches tosses over to first base.
But yet it's still done. Does it have a purpose even if they aren't catching the runners getting too greedy with their lead very often?
John Dewan says yes (h/t BBTF). When looking at data from 2002-2009, they've found that a runner's stolen base percentage actually does decrease when one throw to first base has been made. It goes down slightly with each throw after that, but not significantly. Check out his post for the numbers.
Runners steal at a 65% clip against Pettitte and Burnett which means the league is ineffective by sabermetric standards at swiping with them on the mound. Whether we like it or not, all those throws to to first base do serve a purpose (besides just slowing down the game).