Tesla joining the S&P 500 Friday is ‘mother of all’ stock-market events MarketWatch 12/18/2020 Popular Searches Wall Street will soon find out, as investors strap in for what could be a frenetic ride in equities thanks to electric-vehicle maker Tesla. On Dec. 21, Tesla’s planned inclusion in the granddaddy of the benchmark U.S. stock indexes is set to create what Howard Silverblatt, senior index analyst for S&P Dow Jones Indices, described to MarketWatch as “the mother of all” stock market rebalancing events. An event that will alter the topography of the S&P 500 at a pivotal time in an already tumultuous period in financial markets.