This is not a liberal reporter making the claim. It's a Breitbart reporter and Fox News Contributor.
The rough-up-er was Trump campaign manager Corey Lewandowski. The rough-up-ee was Michelle Fields.
From TV Newser...
A witness told Politico Lewandowski “forcibly grabbed” Fields on the arm, “moving her out of the way and nearly bringing her down to the ground.” The witness said Fields was “clearly roughed up.”
Breitbart News has released a statement, calling the incident “unacceptable” and demanding an apology:
“It’s obviously unacceptable that someone crossed a line and made physical contact with our reporter. What Michelle has told us directly is that someone “grabbed her arm” and while she did not see who it was, Ben Terris of the Washington Post told her that it was Corey Lewandowski. If that’s the case, Corey owes Michelle an immediate apology.” – Larry Solov, Breitbart News CEO and President