One day during shooting, the stuntman needed for various scenes called in sick. There was no time to bring in another stunt double to the location in Mexico, so Rod Taylor, Richard Harris and Al Lettieri convinced the director they could do the stunts themselves. Harris wound up scraping off several inches of skin while making a tackle and Lettieri broke a finger by smashing through a door.
Riding at a full gallop, Taylor was required to fall off his horse, which he did, and it was lucky that director Shear got it in one take because Taylor suffered a dislocated shoulder.
This film began its life as a Samuel Fuller novel called Riata. Fuller then put a lot of work into a screenplay version of the story, and after completing Tote Taube in der Beethovenstraße (1972), he was lined up to shoot Riata in Spain. Shooting began, but after five weeks and spending nearly $1M, Warner Brothers shut the movie down citing "production difficulties" after seeing the dismal rushes featuring a French actress who couldn't act (and who was forced onto Fuller by the shady producer). The rights to the film were sold off, the film was entirely re-written and re-cast, with the exception of Richard Harris, and The Deadly Trackers (1973) is the finished result.
In its original incarnation, Samuel Fuller had lined up Juliet Berto and Mick Jagger. Jim Morrison of The Doors was also lobbying for a role in the film, but was turned down by Fuller.
This originally started life as a Samuel Fuller film with Richard Harris and Bo Hopkins. Filming had begun, but Warner Brothers were so unimpressed with the first rushes, that they shut down the production, and retooled it completely.