“I kill a man and most people understand and forgive me. However, I love a man, and to so many people this is an unforgiveable sin.” Terence Blanchard’s “opera in jazz” for Opera Parallèle and SFJAZZ about Emile Griffith takes this quote by the boxer as its central theme. Blanchard and librettist Michael Cristofer follow Emile’s life from his abusive childhood through his early career as a hatmaker, his training as a boxer, his discovery and exploration of his bisexuality, and his accidental killing of his opponent Benny Paret in a bout. Emile continues racking up victories, but he also suffers brain injury, made worse when he is jumped and beaten outside of a gay bar. He slips into disability and dependence, struggling to perform basic tasks and troubled by vague memories of his past.

Champion uses the idiom of modern opera more than that of jazz, to its detriment. Its most compelling musical moments come when the speak-singing gives way to fully blown arias and jazz numbers. Outside of those, music and lyrics are arbitrarily complex, with plenty of melismas, rhymes, and long lists of synonyms, but no driving force. Frequent unmotivated repetition of large chunks of text slows down the plot. The scoring for both an orchestra and a jazz trio produces an engaging variety of sound. Conductor Nicole Paiement leads the instrumentalists in a tight, balanced rendition of Blanchard’s rhythmic score, which manages to fill the acoustically problematic theater.

The vocal writing is challenging, and the performers shine. As young Emile, bass-baritone Kenneth Kellogg gives an uneven performance: initially underpowered, but eventually rich and moving. Baritone Arthur Woodley, who plays older Emile, has a clear, earthy tone and a touching earnestness in his quest to remember and be forgiven for his past. Robert Orth captivates with his expressions and gestures as Howie Albert, Emile’s abrasive trainer, particularly during his second-act aria about (un)truth in newspapers. But the opera’s star is undoubtedly Karen Slack, who plays Emile’s mother. She gets two stow-shoppers: a jazzy piece with a catchy tune and punishingly wide intervals, and a soaring sad aria about her past. She nails both styles, displaying extraordinary vocal agility and a powerful instrument with a wide range of colors.

Smaller roles are also well-filled. Chabrelle Williams makes a brief but touching appearance as Emile’s neglected wife Sadie. In the role of the abused little Emile, Moses Abrahamson shows off a pure and precise unbroken soprano. Andres Ramirez is an empathetic, gentle Luis (Emile’s caretaker), and Victor Ryan Robertson brings vigor and versatility to the parts of the taunting, homophobic boxer Benny Paret and his wiser, more likeable son.

In contrast to the skill of the individual performers, the crowd scenes lag. While the chorus sings and rhythmically chants with both accuracy and energy, director Brian Staufenbiel seems unsure of what to do with them onstage. Numbers that should be exciting, like the exuberant introduction of young Emile, consist of little more than colorful costumes and hip gyrations. The bit at Hagan’s bar is excruciatingly awkward because all of the intimacy is very obviously faked: what should be a scene of sexual freedom instead resembles a middle-school dance.

Champion offers moments of great lyricism, a lavish orchestral score that is well-delivered, and a talented cast of soloists. But the lyrics, vocal writing, and blocking all stumble, preventing this opera from achieving a knockout.