NFL Officials -- We Investigated Josh Brown for 10 Months ... Wife Wouldn't Comply

The NFL says it can explain why it only suspended Giants kicker Josh Brown for 1 game -- despite the fact his wife claimed he got violent with her on 20 different occasions ... and attacked her while she was pregnant.

NFL investigators say ... they became aware Brown was arrested for an incident involving his wife in May 2015 -- and immediately launched an investigation.

FYI, in the May 2015 police report ... she told cops she had to lock herself in the bedroom to hide from Brown and was really scared. She told police Brown had a history of violence that went back years -- including a 2009 incident when he pushed her while she was several months pregnant.

One of the main issues, according to the NFL, Brown's wife refused to talk to league investigators -- despite multiple attempts.

The NFL says it also tried working with local law enforcement to get information on the case and the previous allegations -- but cops shut them down.

"As a result of these factors, our investigators had insufficient information to corroborate prior allegations."

The NFL points out that no criminal charges were brought against Brown -- so the league was forced to make a decision on discipline "based on the evidentiary findings around [the May 2015] incident as provided to us by the District Attorney."