Chicken will release juices naturally.  There are a few reasons why yours might release more than normal. The chicken you bought has added solution. This is very common and should be listed on the package. The dish is too crowded. The more crowded the dish is, the less liquid will evaporate in cooking. Try using a bigger dish to give your chicken more room to breathe. The chicken cooked too long. As I mentioned above, I like to use thin chicken breasts which allows it to cook more quickly and evenly. If you cook too long the juices will continue to release and the meat will be more dry.  Try using a digital meat thermometer. They are affordable and can be found at almost any store. Cook the chicken just until it reaches an internal temp of 165˚F then remove it from the oven regardless of whether it takes more or less time than directed. The pineapple wasn't drained well. If you don't drain the pineapple well, especially if you use crushed pineapple instead of rings, you can have excess juice in the bottom of the pan