The facts and inferences underlying the officer's suspicion must be viewed as a whole when assessing the reasonableness of his acts. United States v. Cortez, 449 U.S. 411, 417-418 (1981). However, the defendant's flight from the officer's pursuit cannot be considered for this purpose. Stops provoke constitutional scrutiny because they encumber one's freedom of movement. Pursuit that appears designed to effect a stop is no less intrusive than a stop itself. In other words, the officer's right to pursue when a stop appears imminent can be no broader than his right to stop. Thus, his suspicion must be reasonable before the pursuit begins. Were the rule otherwise, the police could turn a hunch into a reasonable suspicion by inducing the conduct justifying the suspicion. For present purposes, a stop starts when pursuit begins. [Cites].

Thus, the reasonableness of the officer's suspicion must be assessed on the basis of two factors: the defendant's use of a bicycle and his sudden left turn.

These circumstances are probably less suspicious than those in Commonwealth v. Bacon, 411 N.E.2d 772. There two young-looking men drove by the police in a relatively expensive car on a Saturday morning about 4:10 A.M. The operator obstructed his face from view with his hand. The officers testified that, in whole or in large part, they stopped the car for running a red light. However, the trial judge disbelieved their testimony that a traffic violation had occurred. We held the stop unjustified, though we noted our reluctance to rule that concealing one's face, combined with other circumstances, could never warrant an investigatory stop. Here, all we have is a quick maneuver on a bicycle. No other circumstances are in the record. This maneuver, however dramatic, cannot rise to the level of suspiciousness justifying an investigatory stop.