Before the Battle of Kumeyki, he brought 500 horsemen and 300 infantry to the army lines. During the campaign, field hetman Mikołaj Potocki ordered Łaszcz's command to provoke the Cossacks to abandon their positions and pursue him. Łaszcz successfully carried out his orders, helping to bring about victory over the more numerous rebels. In 1638, he led his own command against the Cossacks and gained even greater military fame.