MAYOR NUTTER yesterday kicked up a bit of sand in the race for City Council at large when he endorsed an independent candidate.

That sand, apparently, landed in the eye of the Democratic political establishment.

U.S. Rep. Bob Brady, the city's Democratic chairman, said that Nutter, as a ward leader, violated party rules, which state that ward leaders are not permitted to endorse non-Democrats.

"Our party rules say that you can't endorse somebody who is not a Democrat," Brady said yesterday. "He is a ward leader, so he shouldn't be doing that."

Nutter's endorsement of independent at-large candidate Andrew Stober, who recently switched his party affiliation from Democrat so he could run in the Nov. 3 election, was not a surprise.

Stober, who created Indego bike-share, worked for Nutter as a top transportation official.

"It's very, very important that we support strong, intelligent, focused members of City Council," Nutter said at a news conference inside City Hall.

Nutter added, "Based on experience, based on track record, based on the ability to get things done, I am very, very strongly supporting Andrew."

Former Gov. Ed Rendell also threw his support behind Stober yesterday.

Of the Council races, the at-large contest holds the most political intrigue, with new and energized candidates like Stober trying to topple two Republican incumbents, David Oh and Dennis O'Brien.

For voters who have not paid close attention to the Council races, here's a primer:

There are 17 members of Council. Of the 17, 10 seats go to district candidates. This year the district races are ho-hum because only three of the 10 races are contested and those races are not exactly on fire.

The remaining seven seats go to at-large candidates. Five of the seven seats are expected to go to Democrats, given that registered Democrats far outnumber Republicans in Philly. (Nutter also endorsed incumbent at-large Council members Blondell Reynolds Brown and Bill Greenlee.)

Under city election law, two of the seven seats are set aside for minority party candidates. In recent years, Republicans have won the spots. And here's where the election could get interesting.

Voters can pull the lever for up to five at-large candidates, no matter their party registration.

Stober is one of seven minority-party candidates, including three Republicans, looking to unseat Oh and O'Brien. Some political observers view Oh and O'Brien as vulnerable, although they were the two top vote-getters in May's Republican primary.

Indeed, Nutter's endorsement of Stober seemed, in part, like a swipe at Oh and O'Brien. And yet, both Republican and Democratic leaders said they didn't see it that way.

Oh said he thought it was a good thing that Nutter endorsed Stober.

Joe DeFelice, executive director of the Philadelphia Republican City Committee, said he viewed Nutter's support of Stober as a slight to the Democratic candidate slate.

"Mayor Nutter is saying that he will not vote for one of the Democrats," DeFelice said. "That's what he is saying. He has five votes, so he is not going to vote for one of the Democrats if he is supporting an independent."

Nutter's spokesman, Mark McDonald, balked, saying that the mayor has endorsed all five Democratic nominees and by endorsing Stober, he hopes to open the door for Stober to capture a sixth spot.

"He sees this as an opportunity to get a progressive, a strong supporter of Democratic principles, on to City Council in a sixth seat," McDonald said. "The mayor clearly supports the five at-large [Democratic] candidates. Today he endorsed three of them - three who asked him, three with whom he has worked for years and knows them very well."

In addition to incumbents Brown and Greenlee, Nutter yesterday endorsed Democrat Derek Green.

In the 52nd Ward, Nutter presides over 30 Democratic committee people representing 16 divisions within the Wynnefield and Overbrook neighborhoods. Congressman Brady said the Democratic-policy committee will meet and decide whether to "sanction" Nutter for endorsing an independent.

"We can take his ward leadership away," Brady said.

On Twitter: @wendyruderman