Commits a faux pas at the bridge table

• Backs out of, with "on"
• Breaks a promise
• Breaks one's promise
• Fails to keep a promise
• Goes back on one's word
• Breaks promise
• Goes back (on)
• Makes a bridge violation
• Defaults, as on a promise

Wiktionary Word definitions in Wiktionary
vb. (en-third-person singular of: renege )