Needs a look
This might be something as "simple" as a muscle cramp, possibly from dehydration
Or it could be something much more urgent like a deep venous thromboembolism (blood clot
, dvt). Only an examination and workup will be able to determine the cause. Is your calf swollen, especially hot or cold, or hardened (as opposed to soft)? If so, you should probably make your way to your local emergency room.
Answer assisted by Thomas Wolski Jr, Medical Student