https://www.freqtrade.io/en/stable/strategy-customization/#pair-locking-example

from freqtrade.persistence import Trade
from datetime import timedelta, datetime, timezone
# Put the above lines a the top of the strategy file, next to all the other imports
# --------

# Within populate indicators (or populate_buy):
if self.config['runmode'].value in ('live', 'dry_run'):
   # fetch closed trades for the last 2 days
    trades = Trade.get_trades([Trade.pair == metadata['pair'],
                               Trade.open_date > datetime.utcnow() - timedelta(days=2),
                               Trade.is_open.is_(False),
                ]).all()
    # Analyze the conditions you'd like to lock the pair .... will probably be different for every strategy
    sumprofit = sum(trade.close_profit for trade in trades)
    if sumprofit < 0:
        # Lock pair for 12 hours
        self.lock_pair(metadata['pair'], until=datetime.now(timezone.utc) + timedelta(hours=12))