게 뭉치다

clump together; band together

뭉치다 is separate things massing into one lump. With food and material it is scrambled egg going clumpy, squeezing something together neatly so it will not come apart, pressing a mass into shape. With the body it is muscles knotting up, described here as a stiff shoulder or a hardened spot. With people it is closing ranks, which is what the line about a political party means.