* NFL season kickoff on NBC draws 21 million Americans
* Clinton speech attracts 7.5 million ABC, CBS viewers
LOS ANGELES, Sept 6 (Reuters) - Former President Bill Clinton fired up the Democratic National Convention and sparked more than 22,000 tweets per minute, but millions more Americans tuned into football than watched him on television.
Some 21 million Americans watched the National Football League's season kickoff game on NBC between the Dallas Cowboys and the New York Giants on Wednesday night, dwarfing the 7.5 million who watched Clinton's lengthy, humorous and detail-heavy address on the ABC and CBS networks, according to Nielsen data.
Audience figures for cable news networks will be available later on Thursday.
NBC said it did cut into the Democratic convention during halftime of the NFL game, and showed part of political anchor Brian Williams' interview with Clinton about President Barack Obama. But viewers missed most of Clinton's live speech.
For those watching, either online or on television, Clinton fired up the Twitterverse, making hashtags like #arithmetic, #bill and #billclinton among the top trends in the United States on Wednesday evening.
Arithmetic also swiftly became a popular word in media and blog headlines after Clinton said: "People ask me all the time how we delivered four surplus budgets. What new ideas did we bring? I always give a one-word answer: arithmetic."
"Bill Clinton: Our Arithmetic Teacher" ran the headline in a blog on MinnPost.com in Minneapolis. Comedy Central's satirical Indecisionforever.com website ran a piece called "The Arithmetic of Bill Clinton's Speech" and the NationalReview.com website posted a column "Analyzing the Clinton-Obama 'Arithmetic.'"
According to Twitter, Clinton racked up 22,087 tweets per minute - below the 28,000 seen for first lady Michelle Obama during her address in Charlotte, North Carolina on Tuesday, but beating Republican presidential candidate Mitt Romney's 14,289 tweets per minute last week by a large margin.
Clinton's Twindex score, which measures how Twitter users feel about a political person on a scale of 1 to 100, rose from 59 to 70 immediately after his 49-minute address.
On cable news networks, Clinton's speech - which ran well past the 10 to 11 p.m. ET prime time hour - polarized political pundits as deeply as his two terms as president had done in the 1990s.
Fox News Channel's senior political analyst Brit Hume said Clinton was "the most talented politician I've ever met." But Hume took issue with the speech calling it 30 percent too long, "a little self-indulgent" and so packed with facts that it may have turned off the average American TV viewer.
On CNN, political analyst David Gergen said Clinton has been "the best political orator in the country" for the past 20 years.
"Wednesday's talk was the best and most influential he has given since leaving the White House a dozen years ago," Gergen added.