Complex sentence: The Russians launched 7,000 troops against the Sandbag Battery, defended by 2,000 British troops beginning a ferocious struggle which saw the battery change hands repeatedly during the attack.
Split into simpler sentences: The Russians launched 7,000 men against the Sandbag Battery, which was defended by 2,000 British soldiers. So began a ferocious struggle which saw the battery change hands repeatedly during the attack.