ASHBURN, Va. -- The transition to the backup took a little while; the big plays went down and the short catches increased. And then it returned to normal and DeSean Jackson once more became a downfield weapon.

Some of that could be the result of the way defenses played Jackson and the Eagles last year. Some of it, though, was a case of Nick Foles getting used to throwing to Jackson downfield. It’s an adjustment Washington quarterback Kirk Cousins must start to make as well. In his one downfield throw to Jackson last week, the ball was underthrown.

During the summer, quarterback Robert Griffin III talked about adjusting to Jackson’s speed and that it was different than most. He’s not only fast; he also accelerates at the top of routes. And if a quarterback doesn’t account for that, it results in an underthrow.

That doesn’t mean it won’t be a completed pass, but the chance for turning a 25-yard gain into a longer one could be lost.

“What’s friendly about DeSean for the quarterback is that he has the ability, if you feel you put too much air underneath the ball, to go track it,” Redskins offensive coordinator Sean McVay said. “DeSean does a really good job stacking a defender and holding his ground so he gives the quarterback a chance to throw him open – or save some room for the quarterback to throw away from the middle safety.”

Foles, based on the stats, took some time to adjust to Jackson’s deep speed when he took over for Michael Vick last season. Of Jackson’s first 16 catches from Foles, nine were for 10 yards or less and only two were for 25 yards or more. But of his next 16 receptions, six were for 25 yards or more and only three were for less than 10.

It’s not like they can’t click without the deep ball. But it is a strength of Jackson’s game. Cousins did not get much work with Jackson this summer and the receiver could not practice Wednesday because of a sprained shoulder. There’s a chance he’ll do more Thursday and Friday. This summer, when it was Griffin throwing to Jackson, McVay said there was one thing that duo needed: repetitions. That’s one thing Cousins and Jackson haven’t had.

“That will be an emphasis in practice this week to make sure I get a good feel for ‘How fast is this guy really?’ But, in watching and seeing all the reps and the work I have done with him in individual, it is hard to overthrow him,” Cousins said. “And as a result, you want to make sure you get the ball up and down and let him go get it. Guys like that, you just want to give them a chance to make plays and go do what they’re paid to do. You don’t want to be a deterrent or slow them down from being able to make our offenses as explosive as I think it’s capable of being.”

Jackson also said it takes practice. But he’s not about to worry if they don’t have their timing down just yet.

“[The quarterback] has to see it,” Jackson said. “I feel comfortable Kirk Cousins will come in and do a great job. As long as the quarterback is in control and making good reads and getting the ball out of his hands, it makes it that much harder on the defense. We all feel Kirk can get the job done.”