Hand radical on the left — also 摆's indexing radical (side-form of 手). Direct semantic anchor: 摆 covers a whole range of hand-actions — to place, arrange, sway, wave, swing. Same radical in 拍, 推, 拉, 摇, 抓 — the entire active-hand family.
Right side 罢 supplies the sound: bà → bǎi with only a tone shift. The traditional form 擺 had 罷 here, simplified to 罢 in 1956 along with all 罷-containing chars. Pure phonetic role; the 'stop, finish' meaning of 罢 has no overlap with 摆's swinging/arranging senses.
