This is interesting. It's a pilot induced oscillation as a result of a fly-by-wire control system not quite being worked on the Gripen fighter prototype---

As gusts hit the plane, oscillated; the test pilot flying the first prototype tries to correct; the correction arrives after it should have and in too great an amount---and in turn makes the next movement of the nose worse and more extreme; as the pilot feels it coming on, he tries to correct---that in turn makes the next one even worse---and so on and so forth.

He survived with a few broken bones, apparently.

From the youtube comments:

"This was on early software that was prone to coming into oscillation with pilot input. Pilot sense overreaction, put stick in other direction, plane overreacts in that direction, pilot pulls back , and so on. This same pilot was later trusted to fly JAS in a Stockholm City airshow where the 2nd case of oscillation and crash occured. He ejected and survived that one too. Software was later revised to reduce the risk for this type of control problem."