Editor's note: A tweet embedded in this story contains vulgar language.
While trumpeting the end of two-year smartphone contracts and device subsidies at Sprint, Claure blasted Legere on Tuesday: "He's been beating up on our employees for way too long."
"That's over," he continued. "We're back and winning customers and we're just not going to let anybody to continue to insult Sprint."
Claure cited a study released Monday by RootMetrics, which put Sprint in third place in overall performance, network reliability and text performance.
Bashing the RootMetrics report, Legere was quick to respond, using barnyard language:
RootMetrics released this statement to CNBC, which read in part:
"We don't typically get involved in back-and-forth commentary between CEOs, and they have no influence on how we conduct our testing, how we analyze the data we collect, nor on our final results. ... We stand by our methodology and our results."
On CNBC's "Squawk Box," Claure said, "We just don't like it when somebody insults Sprint. I guess someone like John Legere, we have to talk to him on the same language and the language he understands and a language he uses pretty well."
He tweeted a meme with Legere's photo Monday night, playing off the Universal movie "Straight Outta Compton." Legere responded Tuesday morning. (Comcast owns NBCUniversal and CNBC).
Legere also tweeted about this article later in the day:
Two weeks ago, Sprint reported a of a penny per share and raised forward guidance. But revenue was short of forecasts.
, Sprint, which posted 57.7 million customers at the end of the quarter, slipped to fourth place among U.S. wireless carriers, falling behind T-Mobile, which reported 58.9 million customers for the period.
Hopes were dashed earlier this month, as the long-anticipated prospect of a merger of Sprint and T-Mobile was scuttled, due to what's perceived as a unfriendly regulatory environment.
In abandoning two-year smartphone contracts, Sprint joined T-Mobile, which did this two years ago, and Verizon, which made similar moves last week. AT&T remains the only major carrier still offering subsidies.
By the end of year, customers of the No. 4 wireless company Sprint will have to pay the full price for their phones or spread the payments out by leasing the device, an option that started last year
Unbundling the service and the device purchase will save customers money, Claure said on CNBC.
Sprint also announced a new iPhone Forever plan, allowing customers to lease their phones for $22 per month, in addition to monthly service fee, and upgrade to new models as they become available.
In a move to provide access the latest technology without having to wait for contract renewals, Claure said: "You have the ability every single time there's a new iPhone ... [to] go to the store, drop off your old iPhone and pick up a new one. That's included in your rate plan."
The $199 subsidized device is a thing of the past, he added.
Japanese telecommunications giant Softbank bought 80 percent of Sprint for $22 billion in July 2013. Claure became CEO a year ago, as the personal choice of Softbank chief Masayoshi Son.
Last week, SoftBank said it acquired 22.9 million additional Sprint shares at a weighted average price of $3.80 each.