By Brendan Hughes
In a post on Facebook, Crawford said he was stepping away from politics after “much soul-searching” and it was “the right decision for me and my family”.
A day earlier, the UUP had issued a press statement in Crawford’s name condemning the disorder in Ballymena.
He was quoted saying that “peaceful protest is a right, but violence, disorder and racism are not”.
A senior source told BBC News NI that Crawford agreed the release, but was subsequently uncomfortable with some of the wording.
“It was the final straw, the nail in the coffin,” the source added, saying that Crawford had found it difficult settling into his MLA role and being at Stormont.
Following his decision to resign, UUP leader Mike Nesbitt described Crawford as a “valued colleague” and wished him well for the future.
Crawford replaced Robin Swann as a UUP assembly member in July last year after he became the MP for South Antrim in the general election.
The selection of Crawford sparked an internal party row which led to Doug Beattie resigning as Ulster Unionist leader, after he had supported another candidate for the job.
Beattie told BBC News NI’s Red Lines podcast the row had left him “bruised” after three years in charge.