Abstract: A method and apparatus for vertically adjusting the stroke of the polished rod of a pumpjack during its operation in a producing well, while detecting abnormal conditions such as gas-off, pump seizure, sucker and separation, gas-lock pounding or fluid pounding. The method and apparatus involves a hydraulic or pneumatic cylinder interposed between the polished rod clamp and the carrier bar of the pumpjack. Abnormal conditions are detected by an electronic device incorporating a pressure transducer which senses fluid pressure changes in the hydraulic or pneumatic cylinder, converts the pressure changes into electrical voltages, and then determines if an abnormal condition is present. If an abnormal condition is sensed, the pumpjack can be stopped, and restarted automatically after a momentary interval in the event of gas-lock or fluid pounding, or manually after inspection by an operator in the event of a more serious condition.