The man (is generally the one) P (who can work very hard) Q (when he must work who) R (can play most heartily when he has the chance of playing) S The correct sequence should be

Since, the sentence starts with a subject, the next statement will carry a relative pronoun connecting the statements. S follows the opening statement. P will be the next statement which is mentioning the other feature of the man. Q will be the next statement as it describes another quality of man. Thus, R will be the concluding statement and thus form a coherent paragraph.

The correct formation would be, ‘The man who can play most heartily when he has the chance of playing is generally the one who can work very hard when he must work’.