December Disappointments: 10 Big Names Troubled Early

Ten stocks kicked off the first trading week of December losing momentum, slashing as much as double digits amid a flurry of company-specific developments viewed negatively by investors.

Meanwhile, Wall Street’s main indices finished higher week-on-week, led by the Nasdaq, up 0.91 percent, followed by the Dow Jones with a 0.5 percent gain, and the S&P 500, inching up 0.3 percent.

This article focuses on the 10 worst-performers last week and details the reasons behind their performance. The stocks were based on the percentage change in their closing prices on November 28 and December 5, 2025.

To come up with the list, we focused exclusively on stocks with a $2 billion market capitalization and 5 million shares in trading volume.

10. Sunrun Inc. (NASDAQ:RUN)

Sunrun dropped its share prices by 13.18 percent week-on-week, as investor sentiment was dampened by a proposal to register nearly 40 million new shares.

In a filing with the Securities and Exchange Commission on Thursday, Sunrun Inc. (NASDAQ:RUN) said that it intends to register 34.7 million shares to its 2015 Equity Incentive Plan (EIP) as well as 4.2 million shares to its Employee Stock Purchase Plan (ESPP), pursuant to the provisions of the said programs.

Investors viewed the plan negatively, as it opens the door to a potential dilution over time.

In other developments, investors cut down positions in Sunrun Inc. (NASDAQ:RUN) amid the looming deadline for tax credits on clean energy investments.

Under the new rules of the One Big Beautiful Bill Act, signed into law last July, homeowners only have until December 31 to have their solar and battery installations completed to qualify for the 30 percent tax credit.

The deadline is expected to prop up sales of clean energy companies, including Sunrun Inc. (NASDAQ:RUN), as customers scramble to secure the subsidies before they expire.

9. WR Berkley Corp. (NYSE:WRB)

WR Berkley fell by 14.12 percent in the past five trading days of the month as investors resorted to profit-taking following the week prior’s surge, while in a wait-and-see mode for more catalysts to spark trading.

On Friday alone, WR Berkley Corp. (NYSE:WRB) lost as much as 7.7 percent following announcements that it sold a 12.5 percent stake to Mitsui Sumitomo Insurance Co., Ltd., pursuant to an earlier signed agreement.

Under the terms, Mitsui, as a significant shareholder, will vote pursuant to the recommendations of the Berkley family, except in circumstances where it will vote the same way regular shareholders vote overall.

Additionally, WR Berkley Corp. (NYSE:WRB) underscored that Mitsui’s stake was purchased from the company’s outstanding shares, and not directly from the Berkley Family or the company. The transaction is expected to close in the first quarter of January 2026.

In other news, WR Berkley Corp. (NYSE:WRB) declared two cash dividends to its common shareholders as of December 15, both payable on December 29.

The dividends would include $1 special cash dividend per share and 9 cents of regular quarterly dividends.