The noteworthy swap of legendary Cardinals player Curt Flood for Dick Allen had ramifications that stretched far beyond the diamond. Flood’s refusal to accept his fate led the way to a series of court battles that eventually ended in the Supreme Court. Flood lost his court case, but his fight led to a new agreement between players and owners. This agreement allowed for arbitration, which opened the door to the abolition of the reserve clause.
If you put aside the massive historical significance of the trade, the actual baseball ramifications would have been interesting as well.