play ball (?.)

• act in concert
• act together
• affiliate
• ally
• amalgamate
• associate
• band
• band together
• be in league
• club together
• coact
• coalesce
• collaborate
• collude
• combine
• concert
• concord
• concur
• confederate
• consolidate
• conspire
• cooperate
• do business with
• federate
• fuse
• get heads together
• get together
• go partners
• hang together
• harmonize
• hold together
• hook up
• join
• join in
• join together
• keep together
• league
• league together
• make common cause
• merge
• partner
• pull together
• put heads together
• reciprocate
• stand together
• team up
• throw in together
• tie in
• tie up
• unite
• unite efforts
• work together