What caused lyft's share price to tumble after its IPO?

The underwriters overpriced the company at $72 per share when the indicative range was $62 - $68. Given how it made a loss of $900 million in 2018, many find the share price unjust given the uncertainty of it's future propsects (when will it turn profitable) and hence the push down in share price with the short-sells as what Sandra has mentioned.

Lyft's share price tumbled due to the large short-selling interest on the second day of trading. The IPO price was higher than usual due to early enthusiasm from early investors. On the first day of trading, the share price spiked as investors bought with simple buy orders instead of limit buy orders. On the second day of trading, the pre-IPO investors shorted causing the price to go down. The pre-IPO investors were supposed to keep their stock for six months (lock-up period*) but they were allowed to hedge their position, meaning they can sell short as many shares as they own while keeping their shares.

*The lock-up period is meant to avoid flooding the market with more shares than investors want to buy preventing the share price from falling.