Strategist Ryan Detrick on how historical indicators can help predict S&P 500 performance

The double-digit market gains of the first half of the year have some investors wondering if there's any more upside ahead in 2021. Ryan Detrick, senior market strategist at LPL Financial, joined "Squawk Box" on Thursday to explain why he expects the S&P 500 to do well in the second half of the year.