Instead of nodding her head or tapping her feet, Sharel Cassity stands still onstage and lets the music coming out of her horn do the dancing. Cassity, an alto saxophonist, doesn’t dress up her stuff in heavy concepts or abstract rhythms, either. She’s a straight-ahead, bop-based jazz player with a sound that both echoes the hard-edged virtuosity and sometimes violent swing of Charlie Parker and Sonny Stitt, yet hints at the thick, foamy tones of older grandmasters like Johnny Hodges. In short, Cassity is a fantastic player who’s firmly anchored in the tradition, making her an ideal choice to perform at the Kennedy Center’s Mary Lou Williams Jazz Festival, which spotlights women from all walks of jazz. But if she’s remarkably stolid while playing there, don’t be deterred: She doesn’t need to move to move you. Sharel Cassity performs at 6 p.m. at the Kennedy Center Millennium Stage, 2700 F St. NW. Free. (202) 467-4600. kennedy-center.org.