Why would interlacing happen when rendering from 1920×1080 to 720×480

I rendered an .mov from a Premiere CS6 project that is set for 1920×1080 and 23.976 fps. When I rendered it with the NTSC 24p widescreen setting to 720×480 I noticed a lot of interlacing that I did not see before in the project or on another render that I did with a setting of quicktime 1920×1080 with h.264 encoding with 23.976 frames per second. Is there any reason why I would notice interlacing now in the 720×480 version. I’m new to this, so any help is much appreciated. Thanks!

via Adobe Community : Popular Discussions – Adobe Premiere Forums http://forums.adobe.com/thread/1116069