Call volume accelerated on AvalonBay Communities, Inc. (AVB - 137.46) yesterday, as 1,656 contracts changed hands -- nearly quadrupling the stock's typical daily activity. By contrast, only 360 puts were exchanged during the course of Wednesday's session.

Taking a closer look at the day's major block trades, one speculator initiated a ratio call spread on AVB. The trader purchased a block of 500 October 140 calls, and simultaneously sold 1,000 October 150 calls. By selling twice as many calls as he purchased, the spread strategist was able to initiate this bullishly biased play for a slim net debit of just $0.30. So, as long as AVB rallies north of $140.30 (bought strike + net debit) prior to October expiration, the trader stands to make a profit.

However, if AVB rises above $150 over the next seven months, losses could add up quickly. That's because only half of the sold calls are hedged by purchased calls. The best-case scenario here is for AVB to settle squarely at $150 upon October expiration. This will reap the maximum profit of $9.70 on the purchased calls (difference between strikes, less net debit), while the sold calls could be left to expire worthless.

On the charts, AVB's long-term uptrend remains intact, with the stock up more than 20% over the past 52 weeks. Since July 2011, though, the looming $140 level has served as a technical ceiling -- which could explain why Wednesday's spread strategist bought plenty of time for his bullish view to play out.