Before submitting a bug with just “it crashes” in the message body, please look through the Troubleshooting Android development page first.
At this point there are no advanced debug tools to investigate on-device app crashes. However you can use adb application (found under Android-SDK/platform-tools) with logcat parameter. It prints status reports from your device. These reports may include information related to the occurred crash.
If you are sure that the crash you’re experiencing happens due to a bug in Unity software, please save the adb logcat output, conduct a repro project and use the bugreporter (Help/Report a bug) to inform us about it. We will get back to you as soon as we can.