Do condominium owners have to pay for improvements?

Depends on how big the group is. Under Massachusetts General Laws Chapter 183A, Section 18(a), if 50% of the condominium unit owners, but less than 75%, agree to the improvement, only those who agree are required to pay for it.  However, Section 18(b) states:
 
Seventy-five per cent or more of the unit owners may agree to make an improvement to the common areas and facilities and assess the cost thereof to all unit owners as a common expense, but if such improvement shall cost in excess of ten per cent of the then value of the condominium, any unit owner not so agreeing may apply to the superior court of the county in which the property is located, on such notice to the organization of unit owners as the court shall direct, for an order directing the purchase of his unit by the organization of unit owners at fair market value thereof as approved by the court. The cost of any such purchase shall be a common expense.
 
I doubt your share of the tennis court expense would exceed 10% of your unit, but if it does, you can take advantage of the above buy-out clause.  Good luck.