Digital-media entrepreneur and self-styled day trader Dave Portnoy said he purchased about US$10 million worth of Tesla Inc. shares on 7 July after the electric-vehicle maker’s stock fell earlier in the session. Portnoy did not disclose the exact number of shares acquired or the price paid, but described the move as a vote of confidence in the company amid the intraday slide. Tesla shares had been under pressure in morning trading, prompting retail-trading chatter about buying the dip.