Answer:
demand; increase
Step-by-step explanation:
Given that two items are substitutes, consumers tend to be indifferent in using or consuming either one of them. Thus consumers will tend to buy the cheapest among them.
Thus, if the prices of football tickets rises, all else being equal, demand for its substitute (basketball tickets) will increase as consumers shift their purchase to the less expensive substitute.
Therefore, an increase in the price of football ticket will cause the demand for basketball tickets (a substitute) to increase.