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Pfaff started as a high school coach, and moved up to the college ranks starting at Wichita State University. He then served as a graduate assistant at the University of Houston from 1980-81 under Tom Tellez. Pfaff was then Women's Head Track and Field coach at U.T.E.P. from 1982-84. From 1985 to 1994 Pfaff was the head field events coach at L.S.U., during which time the program won multiple national championships, including back to back men's and women's national titles from 1989-90. He then had assistant coaching stints at the University of Texas and the University of Florida..
From ???? he was hired to run the United States Olympic Training Center. In summer 2009, Pfaff was made head of the Lee Valley Athletics Centre by United Kingdom Athletics (UKA), to organise the coaching and training of the UK's athletes in the run-up to the 2012 London Olympics. Pfaff also coached and trained 10 athletes within the UKA programme. Pfaff is currently one of the coaches at the World Athletics Center in Phoenix, Arizona.
Pfaff has coached: Donovan Bailey; Bruny Surin and Glenroy Gilbert—who teamed with Bailey to win the 4 × 100 m also in Atlanta; Greg Rutherford who won the London 2012 Olympics in the men's long jump.