The US version of this camera (The SD880) has a 'kids and pets' mode and I believe the IXUS 870 has that mode as well. This mode is designed to have the same effect of being able to capture moving subjects more quickly. However, depending on your light situation when shooting something in sports, you may need to make more adjustments.
Unfortunately, I don't believe this mode is something that can be quickly accessed on the dial. You need to access the menu.