Following my trailer reaction, it interests me as a former English prof to analyze the official movie synopsis:
Spenser (Mark Wahlberg) — an ex-cop better known for making trouble than solving it — just got out of prison and is leaving Boston for good. But first he gets roped into helping his old boxing coach and mentor, Henry (Alan Arkin), with a promising amateur. That’s Hawk (Winston Duke), a brash, no-nonsense MMA fighter convinced he’ll be a tougher opponent than Spenser ever was. When two of Spenser’s former colleagues turn up murdered, he recruits Hawk and his foul-mouthed ex-girlfriend, Cissy (Iliza Shlesinger), to help him investigate and bring the culprits to justice. From director Peter Berg, SPENSER CONFIDENTIAL is an action-comedy co-starring Bokeem Woodbine, Marc Maron, and Post Malone. Inspired by Robert B. Parker's Wonderland, a best-selling novel by Ace Atkins.
better known for making trouble than solving it - Well, the Spenser of the books was fired for insubordination.
Hawk...a brash, no-nonsense MMA fighter - This version of Hawk is analogous to Parker's character Z(ebulon) Sixkill, created to be Spenser's apprentice in an aborted TNT reboot as the TV rights to Hawk were tied up elsewhere.
Parker brought Z to the books with his 2011 final Spenser novel, Sixkill, and Atkins continued his arc with Wonderland. In the books, Spenser brings Sixkill to Henry to improve his endurance and fighting skill. In the movie, Henry brings Hawk to Spenser to learn boxing, improving his MMA repertoire.
Contrasting Hawk's MMA and Spenser's boxing nods to Duke being fifteen years younger than Wahlberg, better handling than A&E's 1999 movie Small Vices without explanation presenting the similarly younger Shiek Mahmud-Bey as Hawk to Joe Mantegna's Spenser:
foul-mouthed ex-girlfriend - Cissy may be analogous to the books' foul-mouthed Susan Silverman. We see Cissy put up with Spenser, Hawk, and Henry as Susan would. Then again, she could be a lawyer girlfriend before Susan, explaining her helping Spenser investigate.
action-comedy - Seems about the right tone for Spenser. Urich's and Mantegna's portrayals seldom if ever brought the books' humor. Spenser is hard-boiled, not as bleak as noir. If you think Spenser too good a fighter in the books, you may enjoy seeing him knocked down in the trailer. And what movie hero today isn't constantly outnumbered?:
Finally, Inspired by has a looser connotation than "based on," hinting how far Spenser Confidential departs from Robert B. Parker's Wonderland.