The 1892 RLDS edition accidentally omitted the again here; the RLDS text has continued this incorrect reading even though 𝓟 has the again. The use of again is quite correct since the judge had already smitten them on their cheeks:
Summary: Maintain in Alma 14:15 the use of again, the reading of the earliest textual sources; again is appropriate since this was not the first time that the chief judge struck Alma and Amulek on their cheeks.