The wrist digital (or LCD's) came in around he mid 70's.
When I first showed up runners either ran with stop watches or trusted the race directors to get their final times. We didn't always get splits.
I can remember doing intervals using the second hand on a regular watch.
A small company called Microma in Cupertino developed a LCD watch that cost $100. Then they came out with a $50 version. They were spotty at best.
Then Casio (I believe) came out with a cheap but reliable wrist watch with stop watch function and things took off.
By the early 80's these were the rule rather than the exception.