roof, rooftop, pole (for pushing a boat); eaves, cornice; bar, bolt

free-loader, sponge, parasite; shoving, pushing (i.e. a cart or a wheelbarrow)

pushing, butting, collision

butting

butting

accident, collision, incident, chance, coincidence, encounter

collision, accident, clash, skirmish

accident, collision, clash; conflict, contradiction

trip, stumble, crash, collision

confrontation, rivalry, collision