Investors who believe that a stock price will increase over time are said to be bullish. Investors who buy calls are bullish on the underlying stock.That is, they believe that the stock price will rise and have paid for the right to purchase the stock at a specific price known as the exercise price or strike price.An investor who has sold puts is also considered to be bullish on the stock.hat is, they believe that the stock price will rise and have paid for the right to purchase the stock at a specific price known as the exercise price or strike price. An investor who has sold puts is also considered to be bullish on the stock.