The word backswimmers is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 31
Highest Scoring Words With Friends™ Play In The Letters backswimmers
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Seven Letter Word Alert: (34 words)
abscise, ambries, arcwise, ascribe, backers, bammers, beswarm, bickers, braises, cambers, embarks, icemass, kaisers, maimers, maskers, mismake, mismark, racisms, rebacks, reskims, sackers, scabies, screams, scribes, seasick, simmers, skimmer, skiwear, smacker, swamies, swimmer, wackier, webcams, wickers