Why does my boyfriend get protective over me when we are with his friends?

They're all great guys and we are pretty close but when we are all together my boyfriend seems a little on edge. One of his friends today picked me up and threw my over his shoulder and my boyfriend picked me off of him and held me bridalstyle instead. He always intersects with an awkward three person hug if one of them and I are having a good hug. What's his issue?
Why does my boyfriend get protective over me when we are with his friends?
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