Musing on David Robertson's changeup

For the 8th inning of the Yankees' 5-4 win over the Rays on Monday, David Robertson came on and struck out two batters, something that is fairly typical for him.  However, both strikeouts came on a changeup, which is the least frequently used of Robertson's three pitches.  Given that his shutdown eighth was a big moment in the game and many people were watching, now is probably a good time to discuss D-Rob's change:

• Robertson has thrown 20 changeups this year, and 19 of them have been to left-handed batters (the exception was to Nelson Cruz on April 15th).
• It might not sound like a lot, but it's plenty more than he threw last year (five all year, and just one from June through August). 
• At just under 87 mph, it's only about six off of his fastball, but it does have about eight inches more armside tail (something batters are not used to seeing from Robertson, who throws a cutting four-seam fastball and does not use a sinker).
• He doesn't like using it in save situations; he usually only throws the change when behind, tied, or with a big lead (more on this later).

Like I said, Robertson has only thrown 20 changeups this year, so take the numbers below for what they're worth; basically, he misses with it a lot, and when he doesn't, batters do.

mph	#	LHB	RHB	Ball	Called	Swinging	Foul	In Zone	In Play
86.8	20	19	1	11	1	5	3	5	0

Now returning to the fourth bullet-point: Robertson has shown an unwillingness to stray from his two more comfortable pitches in save situations.  The chart below shows the situation in which he threw each of his changeups.

Date	Inning	Balls	Strikes	Score (ahead/behind)
4/2	6	0	0	A-6
4/2	6	1	0	A-6
4/15	5	2	0	B-3
5/7	7	0	1	B-2
5/7	7	1	0	B-2
5/7	7	2	1	B-2
5/7	7	3	2	B-2
5/14	7	1	0	B-6
5/15	7	0	0	B-1
5/15	7	0	1	B-2
5/17	7	1	0	A-3
5/28	7	0	1	Tie
5/28	7	1	0	Tie
5/28	7	0	0	Tie
5/28	8	0	0	Tie
6/16	8	1	1	Tie
6/29	8	0	0	A-3
7/18	8	1	2	Tie
7/18	8	0	2	Tie
7/18	8	1	2	Tie

Only two of his changeups have been thrown in save situations, though that doesn't necessarily mean that he's not comfortable using it in big spots, given his reliance on it in tied games such as yesterday's.  He's proven that he really doesn't need more than two pitches to be lights-out as a reliever, but being able to show the changeup to lefties, as he did yesterday, will make him nastier than he already is.