Cash drag is a diminution of return caused by a cash position in a mutual fund. A mutual fund typically holds a cash position to facilitate redemptions and pending investments. Since underlying securities of a mutual fund, especially stocks, often have better long term returns than cash, a cash position tends to reduce the performance of the fund.
Monthly reporting of mutual fund cash positions are posted at ICI: Trends in Mutual Fund Investing .
Annual cash balances for US equity, balanced, and bond mutual funds are provided in the table below.