Bingo, you can’t claim probable cause based on something you found after you searched a person you detained, because you needed the probable cause BEFORE you detained them in the first place.
The probable cause for the search was a known drug dealer fleeing from police. A dealer who had just been observed making a hand to hand transaction.
Unfortunately you are wrong on this. You go by the totality of the circumstances. Freddie was in an area known for drug trafficking, he had a history of selling drugs and was known to a couple of the officers. He was observed in a hand-to-hand transfer of “something” with another male.
When Freddie saw the cops, he took off running as did the other subject. This is what the Supreme Court has ruled to be “reasonable suspicion” that a criminal act has taken place. The police have every right to pursue Freddie and initiate an investigation. As a result, they found the knife during the pat down. (Terry V Ohio) The knife, which they believed to be illegal under Baltimore City Code was the “probable cause” to arrest Mr. Grey.
There are multiple things going on here and a chronology of events. You do not need “probable cause” to initiate an investigation if the totality of the circumstances would cause a reasonable person to believe a crime had been committed.