A year after a controversial and racially fraught incident in which Newton police formed a barrier between fans and Boston Marathon runners, the Boston Athletic Association says it plans to add four additional miles of barricades to keep spectators off the course route.

The incident happened in Newton at mile 21 of the marathon. Spectators from the PIONEERS Run Crew and TrailblazHers Run Co. were running along part of the course as members of their clubs competing in the marathon passed by. The BAA notified Newton police, who responded to the scene. Videos and photos of the event show about a dozen police officers with bikes lined up along Commonwealth Avenue, facing the spectators in the two running clubs and forming a barrier between them and the course route, as members of the groups questioned why the officers were there.

Both groups are dedicated to spreading the love of running within communities of color. At the time, members of the clubs suggested their cheering area was disproportionately policed. Leaders of both groups did not respond to multiple interview requests for this story.

BAA President and CEO Jack Fleming said the BAA has since held meetings with both running groups. He blamed the problems last year on a failure by the BAA to adequately communicate the need for fans to stay off the course.

“The responsibility on communicating is on the Boston Athletic Association,” Fleming said. “And we didn't do a good enough job communicating what we ask to happen. And that is, with 30,000 participants, we need to ask for a clear course.”

He added that the athletic association has changed its process for how to handle calls that come in from the course on race day.

“Lots of these things are informed by our meetings with the TrailblazHers and PIONEERS Run Crew. They've helped us. We hear them. And we continue to hear them,” he said.

Fleming said each year, the BAA evaluates where additional barricades may be necessary. This year, the four additional miles of barricades will be added in Natick, Wellesley, Framingham and Newton.

“The barricades are a visual reminder that demark, delineate, show everyone easily where the course is and where the sideline is,” Fleming said.

The Newton police chief said after the incident that officers “respectfully” and “calmly” responded to the complaint from the BAA. Fleming did not confirm a recent report in the Boston Globe that the president of the Metropolitan Law Enforcement Council said its members would not staff this year's marathon without an apology from the BAA over its public comments after the incident. But Fleming did acknowledge that he issued an apology.

“In the follow up to last year, I, at the Boston Athletic Association, did not put everyone in the best position,” Fleming said. “So I apologized to the police for the position that they were put in, that I put the police in.”

GBH News has reached out to the head of the Metropolitan Law Enforcement Council for comment.