Brian (not his real name) suffers from deuteranopia, colorblindness where he perceives blue at short wavelengths, see yellow at long wavelengths, and has a neutral point at 498 nm. He has been playing lacrosse and soccer all his life, though he has never been able to see the red lines and markings on all the green fields he has ever played on. Sometimes a story like the above will happen, but he has managed to be a successful player by becoming so accustomed to a field that he knows the general location of all his foul lines. For this post, I asked him to tell me about how his colorblindness makes his playing different from his teammates'. He told me that his challenges are not so much about the lines on the field, but also the jersey colors of the players. He has never had to worry about this at Stockton because their jersey colors are white (home) and black (away). However, on past lacrosse teams and soccer clubs, he has encountered games when one team was green-shirted, and the other red-shirted. This caused trouble for him when playing and passing. He told me the clues that helped him play were elements like differently-shaped helmets, teammates' faces, teammates' calling to him, etc.
Additionally, balls would be difficult for Brian to spot on the field, if they were the correct colors. Luckily between soccer and lacrosse, both playing balls are primarily white, so he has never had a problem seeing them on the field. However, if a ball was red, Brian would have trouble spotting it in a green field.
Although for a trichromat is it difficult to visualize exactly what is seen in Brian's mind's eye, we can only imagine that he uses many other cues to compensate for his difference. When talking to him, he seems open about being a deuteranope and seems to have enough experience on the field to be able to compensate. Although technically a disability, Brian has found ways to live as a deuteranope AND as a successful athlete.