The following contract can be used for sponsorships, without credit.

Sponsorship Contract
Between (insert group name here.) and (insert group name here.)

The following group leaders(insert leader name here.)(insert leader name here.) of the said clubs,
hereby agree to endorse and sponsor each other.
Leaders reserve the right to end the sponsorship at anytime,
with or without the other's permission. By ending the sponsorship,
the said leader will forfeit his/her rights to be sponsored by the
other leader.

Signed,
(insert leader names here.)