This is not the first occasion in which Barnett has been hit in the wallet. He was fined a full paycheck in Week 1 for violating the league's personal conduct policy, stemming from a 2007 off-field incident.
He also was fined $7,500 for a horse-collar tackle in the season opener against the Minnesota Vikings.
"My pockets were a lot lighter from that previous fine and then I got a horse collar on that Monday night game, so it looked like my rookie paycheck this time," Barnett said in the Milwaukee Journal Sentinel.
Barnett found out Thursday that he was fined for the shoulder-to-helmet hit on Kitna.
"Why would I be fined?" Barnett said Wednesday, according to the Journal Sentinel, before he found out he was indeed fined. "He was out of the pocket. He was a running back. How are you supposed to tackle the guy?"
Barnett's fine, which he said he is appealing, should come as no surprise, however. NFL commissioner Roger Goodell issued a sternly worded memo this week to all 32 teams, re-emphasizing safety issues and warning that even first-time offenders would be subject to discipline.
Information from The Associated Press was used in this report.