Flat career

Knock Hard began his career on the flat and developed into a high-class handicapper. In November 1950 he was the subject of a major gamble for the Irish Cesarewitch but was beaten by his stablemate Hatton's Grace after his amateur jockey ignored the trainer's instructions and went to the front too soon. In the following spring he won the apparently competitive Irish Lincoln Handicap over one mile, opening up a clear lead after three furlongs and winning by six lengths.^[3] O'Brien actually admitted that Knock Hard was essentially a flat racer and had "no natural aptitude for jumping".^[5]

1951/52 National Hunt season

Knock Hard had been tried over fences before his win in the Irish Lincoln and in the 1951/52 National Hunt season he developed into a high-class steeplechaser. In December he was sent to race in England for the first time for the King George VI Chase but fell in a race won by the six-year-old Statecraft. He was going well at the time and his rider Phonsie O'Brien (younger brother of the trainer) stated that if he had not fallen he would have won by fifteen lengths.^[5]

On 6 March 1952 Knock Hard made his first attempt to win the Cheltenham Gold Cup and started the 5/1 second favourite in a thirteen-runner field.^[6] Ridden again by Phonsie O'Brien he was closing on the leaders and looked likely to win^[7] when falling at the penultimate obstacle.^[5]

1952/53 National Hunt season

In the late autumn of 1952 Knock Hard returned to the flat and finished second to the three-year-old Summer Rain (winner of the Chester Vase) in the November Handicap at Manchester Racecourse.^[7] He jumped poorly when unplaced behind Halloween in the King George VI Chase and was beaten again when conceding 20 pounds to Mariner's Log at Leopardstown. The horse's performance in the latter race saw O'Brien summoned to appear before the stewards of the Irish Turf Club who suspected that Knock Hard's poor performance had been engineered by his connections to improve his odds in future races.^[3] After two disappointing runs Vincent O'Brien had the gelding examined by a Dublin vet who diagnosed a potentially serious heart problem. O'Brien decided to continue racing the horse but only after explaining the risks to his owner and to his jockey Tim Molony. Knock Hard was back in England in early 1953 for the Great Yorkshire Chase at Doncaster Racecourse and won from the 1952 Grand National winner Teal to whom he was conceding weight.^[5]

On a cold, misty day at Cheltenham on 5 March he made his second attempt to win the Gold Cup. He started at odds of 11/2 against eleven opponents including Halloween (the favourite), Mont Tremblant, E.S.B., Mariners Log and Teal. Knock Hard was not amongst the early leaders and when the horses emerged from the fog approaching the third last he appeared to be out of contention as E.S.B., Mont Tremblant, Galloway Braes and Rose Park disputed the lead. Mont Tremblant soon weakened and Rose Park fell at the second last but Knock Hard began to make rapid progress. He took the lead at the last and drew away up the run-in to win by five lengths and two lengths from Halloween and Galloway Braes.^[3]

Later career, retirement and death

In March 1954 Knock Hard attempted to repeat his 1953 success in the Gold Cup but struggled on the heavy ground and finished fifth of the nine runners behind Four Ten, Mariner's Log, Halloween and Mont Tremblant.^[5]

Knock Hard later was bought by Francis More O'Ferrall. His form deteriorated further and he was given away to Lady Jane Lumley, the daughter of Lord Scarbrough and he was moved to England to become a hunter. He collapsed and died approximately two years later, probably due to a recurrence of his heart condition.^[3]