In many track races you see the leader moving out from lane 1 to lane 2, apparently to make it difficult for the person behind to overtake them. You can see a mild example of this in the video, where the winner comes around the final bend in lane 1 and crosses the line in lane 2, as those behind try to overtake her. Is this cheating of just smart tactics? Given that athletes are rarely disqualified for this behaviour it's hard to know. It used to be that blocking was explicitely allowed. In the 1908 Olympics 400m race, American winner John Carpenter was disqualified from the race for blocking Wyndham Hallswelle, a British athlete and the race was declared void. In the US using your elbows to block an athlete overtaking was considered legal, but in Britain, the host country, it was illegal and the host country rules prevailed.
The winner of the 2012 Olympic Women's 1500m race in the video clip didn't suffer any sanction so it must be legal! However in the 1908 Olympics 400m race Halswelle ran the rescheduled race on his own, as his competitors refused to run in protest at Carpenter's treatment. He thus became the only winner of an Olympic medal by walkover. This event resulted in lanes being used from 1912. He died in WW1, shot by a sniper.