A user may be liquidated if their collateralization drops below 133%. Two liquidation options are available. In a range from 129 - 133% of collateralization, only a closed liquidation is available. In this case, a pre-approved swapper may be called by the SushiSwap team or liquidity providers to swap collateral to asset. The liquidation proceeds are distributed amongst liquidity providers and xSushi holders.
If this range passes without a position being liquidated, it goes into open liquidation. At this point, anyone may liquidate a position by providing the borrowed amount directly or using a swapper of their choosing.