Neurocognitive testing (NCT) and quantitative electroencephalography (qEEG) are brain assessment procedures that are used to investigate relationships between cortical functioning and context-specific outcome measures to arrive at clinical diagnoses or better informed patient and client evaluations. Research is ongoing to test the premise that NCT and qEEG can serve as reliable criterion-referenced measures for athletes profile primary higher order (AP PHO) constellations, heart rate variability (HRV) responding and eventually macro- and micro-performance outcome. Low/high ratio (L/H) was associated with numerous conceptually relevant NCT tests, including motor tapping variability, motor tapping, and switching of attention completion time. This chapter reviews the results from pilot research encompassing over 50 athletes from the sports of baseball, tennis, and ice hockey prior to presenting a case study of an ex-world class professional tennis player who underwent NCT and qEEG as part of the American Board of Sport Psychology-Carlstedt Protocol (ABSP-CP) pre-intervention evaluation process.