Manual Stuck In Gear, Shifter Moves Front And Back Freely Wont Go Left Ot Right

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I put the car in reverse, backed out of my driveway, put the car in 1st, drove down the road, shifted into second, then came to a stop sign. When I tried to shift back into first, the transmission was stuck in second, but the shifter moved vertically back and forth freely, but would not move side to side. The clutch is fine, I started the car back up, and drove back to the house in second gear. I haven't had any gear slippage or shifter / transmission issues leading up to this. Any thoughts? Shifter linkage?