in opposition to

the fight against crime

he decided against immediate publication

swimming against the tide

in anticipation of and preparation for (a problem or difficulty)

he gritted his teeth against the pain

makeshift barricades against tank attacks

in or into physical contact with (something), so as to be supported by or collide with it

she stood with her back against the door

frustration made him bang his head against the wall

in conceptual contrast to

the benefits must be weighed against the costs