Two scenarios

One is where you're walking and all of a sudden a girl is walking against you're direction, I always have this brain freeze or thinking, where before I can even make up my mind about approaching, the girl is already past you. Sometimes the brain freeze is because of an awkward eye contact or something. How can I stop the girl and approach?

Scenario Two: You spot a girl a bit distance away from you walking away from your direction. I start the approach and sometimes I feel like i have to run to catch up. Girls usually walk fast like they're being chased by a predator or something. What would be a good strategy to approach. Should I like run up to her?

And also what are some good openers? I sometimes use, Do you know where I can find you're number? Its kinda too direct.