In the Article is produced analyze of the one of the most reflector functions of Tennis player - Reaction to the moving Object (RMO). On base of statistical studies of 6-9 age children is made a conclusion about close-fitting intercoupling between Reaction to the moving Object and speed ability of a child (coefficient of correlations reaches to 80%). Analyzes showed that there are some defects of vision, which don’t reveal themselves in usual life, but which can greatly reduce the Reaction to the moving Object. These parameters are the factors of the eye's resolution and quality of binocular vision; they both must be checked by special ophthalmologic equipment.