Why do you get nervous when you play basketball with people you dont know?

Answer 1

Humans, by and large, tend to experience a level of nervousness with most strangers, in general. Causes of this response have been argued from both the "nature" and "nurture" perspectives, but the end result is the same: our nervous systems experience swift changes in situations in which we feel a lack of familiarity and/or control.

In the extreme, this is known as the "Flight or Fight" response, which is actually,simply, the activation of the Sympathetic Nervous System (which causes marked changes in bodily function, including metabolic rate, sensory response, mental acuity levels, digestive function, etc.). Activation of the SNS is designed, physiologically, to enhance performance in response to the "threat" by improving those bodily functions that will assist in survival or defense, while inhibiting bodily functions that might be counterproductive (i.e. slowing us down, or preventing us from best responding).

Since sports tend to be inherently competitive, this would serve to enhance the natural stimulation of the sympathetic nervous system. Without getting into too much detail with regard to its affect on neurochemical levels in the brain, suffice it to say that the combination of competition and introduction into unfamiliar circumstances can cause those feelings. It's a biological response to a cognitive assessment.