Many studies have reported physiological and cognitive decrements following heat stress. Of particular concern in cricket are the possible negative effects of sustained protective helmet use, as this leads to an increase in heat-related stress. Correct and rapid decision making, and focused attention are essential for efficient performance whilst batting, and it is possible that helmet usage could impair such processes. In a repeated-measures, randomized crossover study, physiological, self-report, and cognitive measures were taken from 16 teenage cricketers before and after moderately intense (batting) exercise. Participants underwent the assessments twice, once while wearing a standard protective helmet, and again, when not wearing a helmet (counterbalanced). While helmet use did not lead to significant physiological changes, wearing a helmet led to some cognitive impairments in attention, vigilance and reaction times. These preliminary findings could have significance for cognitively demanding sports (and perhaps military and industrial settings) in which participants perform cognitively demanding operations under conditions of physical exercise whilst wearing protective helmets. Additional factors of hydration, exercise duration, and helmet design are discussed.