Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Interaction between interlacing and chroma subsampling

To overly simplify the issue:

1. The use of interlacing halves the effectiveness of chroma subsampling vertically.
2. Interlaced 4:2:0 subsamples chroma 2X in both directions.
3. Its effective performance is as if chroma were subsampled 2X horizontally and 4x vertically.
4. On top of that, the chroma has comb-like artifacts (because of interlacing) that require additional image processing to remove.
   
5. In-range reconstruction is much more difficult to achieve?

For more information, see Don Munsil and Stacey Spears’ “The Chroma Upsampling Error and The 4:2:0 Interlaced Chroma Problem”.