Why is it important to warm up before a game or physical activity?

It is important to warm-up before a game or before a physical activity so that your body can get ready for the physical activity and your muscles/bones loosened up. If you warm-up before doing any sort of physical activity, your risks of getting an injury decrease dramatically.
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Yes. If you do not warm up your muscles, there is a much higher chance of pulling/tearing a muscle. I play soccer, and i did not warm up and stretch with my team pre game and i tore my ACL