The basic idea, as I understand it and as most people seem to interpret it, is that every single trade is a potentially taxable event, and the basis/gain/loss is computed using the fair market value at the moment of the trade. Whether a transaction is taxable or not has nothing to do with whether the transaction involved fiat.

You sell 1 ETH for 1 TOKEN on Binance: you're exiting an ETH position and entering a TOKEN position. If you bought that 1 ETH for $50 and then it's worth $500 at the time you traded it for the 1 TOKEN, then you have a (roughly) $450 taxable gain.

Of course, I'm not a tax adviser and this isn't tax advice. Just trying to be a friendly helpful person.