When you look at the diagrams (cladograms) put forward for theropods you see a branch called "maniraptors" which has been tacked onto the theropod line, where it does not belong at all.
See here for an example of a typical diagram:
The creatures labeled "maniraptors" are actually birds (not dinosaurs). They do not belong in the theropod line at all.
Here is a reference to that idea:
"We suggest that a possible solution to the disparate data is that Aves plus bird-like [flightless] maniraptoran theropods (e.g., microraptors and others) may be a separate clade [separate line], distinctive from the main lineage of Theropoda, a remnant of the early avian radiation, exhibiting all stages of flight and flightlessness". (Alan Feduccia 1 *, Theagarten Lingham-Soliar 2, J. Richard Hinchliffe 3)