1 Con may express meeting of two or more persons in a place or in an opinion.
Me crucé con él en la calle y no me saludó.
Coincido contigo: esto es una vergüenza.
2 Con also indicates stumble with an obstacle that stops the walk.
Tropecé con el bordillo. (= The stumbling forces me to stop.)
With the same meaning contra may be used.
Tropecé contra un poste de la luz. (= And the stumbling forces me to stop.)
If the obstacle does not stop the walk the preposition en is used.
Tropecé en el bordillo. (= And I went on my way.)