Sometimes even though the clip displays correctly in the photos app on an iPad it can be rotated when used in iMovie 

It is however possible to rotate a video clip in iMovie

To do so follow the instructions below 

Please note though it can only be rotated in 90 degree increments 

You can rotate a video clip in 90-degree increments, clockwise or anticlockwise.

  1. With your project open, scroll the timeline until the clip you want to rotate appears in the viewer.

  2. In the viewer, move your finger and thumb in a clockwise or anticlockwise twisting motion over the video image.

    When the white arrow appears, the video clip has been rotated 90 degrees. It may take a moment for the clip to appear rotated in the viewer.

    Repeat this gesture as many times as necessary to achieve the orientation you want.

    A clip being rotated in the project timeline.