The sutrah of the imam is the sutrah of everyone behind him.
‘Amr ibn Shu’aib relates from his father on the authority of his grandfather who said: “We were descending on a path near Makkah with the Messenger of Allah and the time for prayer came. The Prophet prayed toward a wall and we were behind him. A lamb tried to pass in front of him and he kept preventing the lamb from doing so until its stomach was up against the wall. Finally, it passed behind him.” This is related by Ahmad and Abu Dawud.
Ibn ‘Abbas says: “I was riding a donkey and was at the time on the threshold of maturity, and the Prophet was leading the people in salah at Mina. I passed in front of the row and let the animal graze, and then I joined the rows and no one objected to this.” This is related by the group.
These hadith prove that it is allowed to pass in front of people following the imam, and that the sutrah is required for the imam and the people praying individually.