I spoke too soon. Sorry – of course it has fields, since it’s 29.97 (60i) on the tape. If you have been given footage that way, you need to remove pulldown before you roto.
So:
1. Import the footage into AE, and set field separation “off”.
2. alt-double-click on the footage and step through it with the pageDn key. If you see interlacing, it’s 29.97.
3. Re-intepret the footage, field sep “lower first”, and remove pulldown — try guessing.
4. do step 2, for about 10 clicks or more. If you see fields, AE guessed wrong, and you need to re-interpret with a different cadence.
5. Once you’ve eliminated the fields that way, drag the footage onto the “new comp” button at the bottom of the project window and go to work.
Did that help?