Not surprisingly there's a healthy correlation between a team's overall record and its "Fighting Loss%" -- after all the good teams should seldom be getting blown out, whereas the less talented teams struggle to keep it close.
This is what makes the Mavericks season so far such an outlier -- with 28 clutch losses out of 40 total losses they are at a 70% Fighting Loss rate. In the past eight seasons, only twenty teams have had a 70%+ fighting loss rate, and only two of these had fewer than 47 wins on the season...the '10-11 Rockets who were 43-39...and the '12-13 Washington Wizards who went 29-53 (and 16-37 in close games).
The top of the list in fighting loss% over this span is dominated by two teams: of the top 12 recorded FL% seasons, Oklahoma City has FIVE of them, Toronto has THREE (and is tops this year so far...OKC's % is down a bit but still 9th best in league).
What explains the consistency of the OKC-TOR runs? Well in addition to talent of the roster, coaching certainly comes to mind -- Scott Brooks did well in this in his time in Oklahoma and has since posted a 70% fighting loss season in '16-17 in Washington and a 63% seventh ranked season to this point in '17-18...meanwhile Dwane Casey is currently the fourth longest tenured head coach in the NBA behind Pops, Carlisle, and Spo...
Still, there are a lot of factors that go into this number, and the overarching one is simply the record in clutch games...had the Mavs won a few more of those this season their fighting loss% would be lower.
How do the "unlucky losers" fare the following season?