clash
Definitions
A violent confrontation or disagreement between opposing groups or ideas.
A mismatch of colors, patterns, or styles that look unattractive together.
To make a loud, harsh, metallic sound by striking together.
Examples
The two political parties had a major clash over the new tax legislation.
I decided not to wear the red shirt with those pants because the colors clash.
The protesters and the police were involved in a violent clash outside the city hall.