This was taken at quite a distance, and is cropped quite a bit, but it came out sorta' okay. This Swainson's Hawk is making off with a kill, and a Red-winged Blackbird is in pursuit. I suspect the hawk might have grabbed a young blackbird.
@Vixen Vixen, there is a button lock, but it also locks by sliding the zoom ring. I know because I had one and had this very same issue. Before you mail it off for repair, check this.
From Tamron: The new FLEX ZOOM LOCK mechanism quickly locks or unlocks the zoom at any position simply by...