Complex sentence: Sifford first attempted to qualify for a PGA Tour event at the 1952 Phoenix Open, using an invitation obtained by former World heavyweight boxing champion Joe Louis and was subjected to threats and racial abuse there and at other tournaments.
Split into simpler sentences: Sifford first attempted to qualify for a PGA Tour event at the 1952 Phoenix Open, using an invitation obtained by former World heavyweight boxing champion Joe Louis. Sifford was subjected to threats and racial abuse there and at other tournaments.