An even better but potentially more expensive option is to get a bunch of mounted men and give them lances. Have them essentially joust at the man in shardplate. Train the horses to be maneuverable, to charge with a lot of weight behind them and you could severally crack the shardplate or knock them over. Then you can essentially do mop up action. After a few passes have several skilled men with war axes do additional damage and then either wait for them to run out of stormlight or have skilled arches put some arrows through the gap. The main problem with shardbears is not that they are impossible for a disciplined and well armed group of opponents to kill it is that they can break formations and cause confusion that their soldiers can take advantage of.