Chiefs/Vikings Fumble

[TexansFan]

In the Chiefs/Vikings game on Dec. 20th a fumble occured near the sidelines and I was wondering if I was correct in my asessment of the play.

The pass was caught in bounds and the Chiefs receiver was running down the sideline. The Viking defender came from behind and stripped the ball loose, batted it in mid-air and the ball was subsequently recovered in-bounds by the Vikings.

The question here is this: The Viking defender was out of bounds when he stripped the ball and was also out of bounds when he batted the ball back into the field of play. My take on it was that the Viking defender being out of bounds on either instance should not matter because the offensive player and the ball were both in the field of play.

The other take that some of my friends have taken is that since the Viking defender was out of bounds during the strip and/or on the batting of the ball back into the field of play, the ball is considered dead at that spot of the strip/bat and possesion would remain the offense (Chiefs).

In the game, the play was ruled a fumble with possession to the Vikings. The ruling was challenged by the Chiefs and after review the call was that the ruling on the field stands.

What is the official NFL ruling on this?