At least a half-dozen top NFL officials waged an improper campaign to influence a major U.S government research study on football and brain disease.

A 91-page report describes how the NFL pressured the National Institutes of Health to strip the $16 million project from a prominent Boston University researcher and tried to redirect the money to members of the league's committee on brain injuries. The study was to have been funded out of a $30 million "unrestricted gift" the NFL gave the NIH in 2012.

After the NIH rebuffed the NFL's campaign to remove Robert Stern, an expert in neurodegenerative disease who has criticized the league, the NFL backed out of a signed agreement to pay for the study, the report shows. Taxpayers ended up bearing the cost instead.

The NFL's actions violated policies that prohibit private donors from interfering in the NIH peer-review process, the report concludes, and were part of a "long-standing pattern of attempts" by the league to shape concussion research for its own purposes.

"In this instance, our investigation has shown that while the NFL had been publicly proclaiming its role as funder and accelerator of important research, it was privately attempting to influence that research," the report states.