Complex sentence: In cycling, the main (largest) group of tightly packed cyclists in a race is called a "peloton", where cyclists ride in a long formation, with each (but not the first one) drafting behind the others before them.
Split into simpler sentences: In cycling, the main (largest) group of tightly packed cyclists in a race is called a "peloton", where cyclists riding in a long shaped formation. Each (but not the first one) drafting behind the others before them.