Complex sentence: There are usually two stone-lifters competing in each event, taking turns in one or several attempts, to perform the greatest possible number of lifts; a lift is considered complete when the stone has been properly balanced on the shoulder.
Split into simpler sentences: There are usually two stone-lifters competing in each event, taking turns in one or several attempts, to perform the greatest possible number of lifts. A lift is considered complete when the stone has been properly balanced on the shoulder.